diff --git a/cmdgen.c b/cmdgen.c
index 50f99f701..5b0e54d9a 100644
--- a/cmdgen.c
+++ b/cmdgen.c
@@ -667,7 +667,7 @@ int main(int argc, char **argv)
 	    return 1;
 	}
 	random_add_heavynoise(entropy, bits / 8);
-	memset(entropy, 0, bits/8);
+	smemclr(entropy, bits/8);
 	sfree(entropy);
 
 	if (keytype == DSA) {
@@ -860,7 +860,7 @@ int main(int argc, char **argv)
 		return 1;
 	    }
 	    if (passphrase) {
-		memset(passphrase, 0, strlen(passphrase));
+		smemclr(passphrase, strlen(passphrase));
 		sfree(passphrase);
 	    }
 	    passphrase = dupstr(p->prompts[0]->result);
@@ -1035,7 +1035,7 @@ int main(int argc, char **argv)
     }
 
     if (passphrase) {
-	memset(passphrase, 0, strlen(passphrase));
+	smemclr(passphrase, strlen(passphrase));
 	sfree(passphrase);
     }
 
diff --git a/cmdline.c b/cmdline.c
index 2c3b7ce5c..a4c916010 100644
--- a/cmdline.c
+++ b/cmdline.c
@@ -63,7 +63,7 @@ void cmdline_cleanup(void)
     int pri;
 
     if (cmdline_password) {
-	memset(cmdline_password, 0, strlen(cmdline_password));
+	smemclr(cmdline_password, strlen(cmdline_password));
 	sfree(cmdline_password);
 	cmdline_password = NULL;
     }
@@ -106,7 +106,7 @@ int cmdline_get_passwd_input(prompts_t *p, unsigned char *in, int inlen) {
 	return 0;
 
     prompt_set_result(p->prompts[0], cmdline_password);
-    memset(cmdline_password, 0, strlen(cmdline_password));
+    smemclr(cmdline_password, strlen(cmdline_password));
     sfree(cmdline_password);
     cmdline_password = NULL;
     tried_once = 1;
@@ -368,7 +368,7 @@ int cmdline_process_param(char *p, char *value, int need_save, Conf *conf)
 	    /* Assuming that `value' is directly from argv, make a good faith
 	     * attempt to trample it, to stop it showing up in `ps' output
 	     * on Unix-like systems. Not guaranteed, of course. */
-	    memset(value, 0, strlen(value));
+	    smemclr(value, strlen(value));
 	}
     }
 
diff --git a/import.c b/import.c
index 55e3be27b..05cfdc147 100644
--- a/import.c
+++ b/import.c
@@ -358,7 +358,7 @@ static struct openssh_key *load_openssh_key(const Filename *filename,
 	errmsg = "unrecognised key type";
 	goto error;
     }
-    memset(line, 0, strlen(line));
+    smemclr(line, strlen(line));
     sfree(line);
     line = NULL;
 
@@ -442,13 +442,13 @@ static struct openssh_key *load_openssh_key(const Filename *filename,
                     memcpy(ret->keyblob + ret->keyblob_len, out, len);
                     ret->keyblob_len += len;
 
-                    memset(out, 0, sizeof(out));
+                    smemclr(out, sizeof(out));
                 }
 
 		p++;
 	    }
 	}
-	memset(line, 0, strlen(line));
+	smemclr(line, strlen(line));
 	sfree(line);
 	line = NULL;
     }
@@ -463,23 +463,23 @@ static struct openssh_key *load_openssh_key(const Filename *filename,
 	goto error;
     }
 
-    memset(base64_bit, 0, sizeof(base64_bit));
+    smemclr(base64_bit, sizeof(base64_bit));
     if (errmsg_p) *errmsg_p = NULL;
     return ret;
 
     error:
     if (line) {
-	memset(line, 0, strlen(line));
+	smemclr(line, strlen(line));
 	sfree(line);
 	line = NULL;
     }
-    memset(base64_bit, 0, sizeof(base64_bit));
+    smemclr(base64_bit, sizeof(base64_bit));
     if (ret) {
 	if (ret->keyblob) {
-            memset(ret->keyblob, 0, ret->keyblob_size);
+            smemclr(ret->keyblob, ret->keyblob_size);
             sfree(ret->keyblob);
         }
-        memset(ret, 0, sizeof(*ret));
+        smemclr(ret, sizeof(*ret));
 	sfree(ret);
     }
     if (errmsg_p) *errmsg_p = errmsg;
@@ -494,9 +494,9 @@ int openssh_encrypted(const Filename *filename)
     if (!key)
 	return 0;
     ret = key->encrypted;
-    memset(key->keyblob, 0, key->keyblob_size);
+    smemclr(key->keyblob, key->keyblob_size);
     sfree(key->keyblob);
-    memset(key, 0, sizeof(*key));
+    smemclr(key, sizeof(*key));
     sfree(key);
     return ret;
 }
@@ -564,8 +564,8 @@ struct ssh2_userkey *openssh_read(const Filename *filename, char *passphrase,
 	    aes_free_context(ctx);
 	}
 
-        memset(&md5c, 0, sizeof(md5c));
-        memset(keybuf, 0, sizeof(keybuf));
+        smemclr(&md5c, sizeof(md5c));
+        smemclr(keybuf, sizeof(keybuf));
     }
 
     /*
@@ -698,12 +698,12 @@ struct ssh2_userkey *openssh_read(const Filename *filename, char *passphrase,
 
     error:
     if (blob) {
-        memset(blob, 0, blobsize);
+        smemclr(blob, blobsize);
         sfree(blob);
     }
-    memset(key->keyblob, 0, key->keyblob_size);
+    smemclr(key->keyblob, key->keyblob_size);
     sfree(key->keyblob);
-    memset(key, 0, sizeof(*key));
+    smemclr(key, sizeof(*key));
     sfree(key);
     if (errmsg_p) *errmsg_p = errmsg;
     return retval;
@@ -911,8 +911,8 @@ int openssh_write(const Filename *filename, struct ssh2_userkey *key,
 	 */
 	des3_encrypt_pubkey_ossh(keybuf, iv, outblob, outlen);
 
-        memset(&md5c, 0, sizeof(md5c));
-        memset(keybuf, 0, sizeof(keybuf));
+        smemclr(&md5c, sizeof(md5c));
+        smemclr(keybuf, sizeof(keybuf));
     }
 
     /*
@@ -936,19 +936,19 @@ int openssh_write(const Filename *filename, struct ssh2_userkey *key,
 
     error:
     if (outblob) {
-        memset(outblob, 0, outlen);
+        smemclr(outblob, outlen);
         sfree(outblob);
     }
     if (spareblob) {
-        memset(spareblob, 0, sparelen);
+        smemclr(spareblob, sparelen);
         sfree(spareblob);
     }
     if (privblob) {
-        memset(privblob, 0, privlen);
+        smemclr(privblob, privlen);
         sfree(privblob);
     }
     if (pubblob) {
-        memset(pubblob, 0, publen);
+        smemclr(pubblob, publen);
         sfree(pubblob);
     }
     return ret;
@@ -1067,7 +1067,7 @@ static struct sshcom_key *load_sshcom_key(const Filename *filename,
 	errmsg = "file does not begin with ssh.com key header";
 	goto error;
     }
-    memset(line, 0, strlen(line));
+    smemclr(line, strlen(line));
     sfree(line);
     line = NULL;
 
@@ -1112,7 +1112,7 @@ static struct sshcom_key *load_sshcom_key(const Filename *filename,
 		len += line2len - 1;
 		assert(!line[len]);
 
-		memset(line2, 0, strlen(line2));
+		smemclr(line2, strlen(line2));
 		sfree(line2);
 		line2 = NULL;
             }
@@ -1158,7 +1158,7 @@ static struct sshcom_key *load_sshcom_key(const Filename *filename,
 		p++;
 	    }
 	}
-	memset(line, 0, strlen(line));
+	smemclr(line, strlen(line));
 	sfree(line);
 	line = NULL;
     }
@@ -1173,16 +1173,16 @@ static struct sshcom_key *load_sshcom_key(const Filename *filename,
 
     error:
     if (line) {
-	memset(line, 0, strlen(line));
+	smemclr(line, strlen(line));
 	sfree(line);
 	line = NULL;
     }
     if (ret) {
 	if (ret->keyblob) {
-            memset(ret->keyblob, 0, ret->keyblob_size);
+            smemclr(ret->keyblob, ret->keyblob_size);
             sfree(ret->keyblob);
         }
-        memset(ret, 0, sizeof(*ret));
+        smemclr(ret, sizeof(*ret));
 	sfree(ret);
     }
     if (errmsg_p) *errmsg_p = errmsg;
@@ -1222,9 +1222,9 @@ int sshcom_encrypted(const Filename *filename, char **comment)
 
     done:
     *comment = dupstr(key->comment);
-    memset(key->keyblob, 0, key->keyblob_size);
+    smemclr(key->keyblob, key->keyblob_size);
     sfree(key->keyblob);
-    memset(key, 0, sizeof(*key));
+    smemclr(key, sizeof(*key));
     sfree(key);
     return answer;
 }
@@ -1390,8 +1390,8 @@ struct ssh2_userkey *sshcom_read(const Filename *filename, char *passphrase,
 	des3_decrypt_pubkey_ossh(keybuf, iv, (unsigned char *)ciphertext,
 				 cipherlen);
 
-        memset(&md5c, 0, sizeof(md5c));
-        memset(keybuf, 0, sizeof(keybuf));
+        smemclr(&md5c, sizeof(md5c));
+        smemclr(keybuf, sizeof(keybuf));
 
         /*
          * Hereafter we return WRONG_PASSPHRASE for any parsing
@@ -1494,12 +1494,12 @@ struct ssh2_userkey *sshcom_read(const Filename *filename, char *passphrase,
 
     error:
     if (blob) {
-        memset(blob, 0, blobsize);
+        smemclr(blob, blobsize);
         sfree(blob);
     }
-    memset(key->keyblob, 0, key->keyblob_size);
+    smemclr(key->keyblob, key->keyblob_size);
     sfree(key->keyblob);
-    memset(key, 0, sizeof(*key));
+    smemclr(key, sizeof(*key));
     sfree(key);
     if (errmsg_p) *errmsg_p = errmsg;
     return ret;
@@ -1664,8 +1664,8 @@ int sshcom_write(const Filename *filename, struct ssh2_userkey *key,
 	des3_encrypt_pubkey_ossh(keybuf, iv, (unsigned char *)ciphertext,
 				 cipherlen);
 
-        memset(&md5c, 0, sizeof(md5c));
-        memset(keybuf, 0, sizeof(keybuf));
+        smemclr(&md5c, sizeof(md5c));
+        smemclr(keybuf, sizeof(keybuf));
     }
 
     /*
@@ -1700,15 +1700,15 @@ int sshcom_write(const Filename *filename, struct ssh2_userkey *key,
 
     error:
     if (outblob) {
-        memset(outblob, 0, outlen);
+        smemclr(outblob, outlen);
         sfree(outblob);
     }
     if (privblob) {
-        memset(privblob, 0, privlen);
+        smemclr(privblob, privlen);
         sfree(privblob);
     }
     if (pubblob) {
-        memset(pubblob, 0, publen);
+        smemclr(pubblob, publen);
         sfree(pubblob);
     }
     return ret;
diff --git a/misc.c b/misc.c
index 636ca9f39..76e5fab21 100644
--- a/misc.c
+++ b/misc.c
@@ -124,7 +124,7 @@ void prompt_ensure_result_size(prompt_t *pr, int newlen)
          */
         newbuf = snewn(newlen, char);
         memcpy(newbuf, pr->result, pr->resultsize);
-        memset(pr->result, '\0', pr->resultsize);
+        smemclr(pr->result, pr->resultsize);
         sfree(pr->result);
         pr->result = newbuf;
         pr->resultsize = newlen;
@@ -140,7 +140,7 @@ void free_prompts(prompts_t *p)
     size_t i;
     for (i=0; i < p->n_prompts; i++) {
 	prompt_t *pr = p->prompts[i];
-	memset(pr->result, 0, pr->resultsize); /* burn the evidence */
+	smemclr(pr->result, pr->resultsize); /* burn the evidence */
 	sfree(pr->result);
 	sfree(pr->prompt);
 	sfree(pr);
@@ -203,7 +203,7 @@ char *dupcat(const char *s1, ...)
 void burnstr(char *string)             /* sfree(str), only clear it first */
 {
     if (string) {
-        memset(string, 0, strlen(string));
+        smemclr(string, strlen(string));
         sfree(string);
     }
 }
@@ -685,3 +685,43 @@ char const *conf_dest(Conf *conf)
     else
 	return conf_get_str(conf, CONF_host);
 }
+
+#ifndef PLATFORM_HAS_SMEMCLR
+/*
+ * Securely wipe memory.
+ *
+ * The actual wiping is no different from what memset would do: the
+ * point of 'securely' is to try to be sure over-clever compilers
+ * won't optimise away memsets on variables that are about to be freed
+ * or go out of scope. See
+ * https://buildsecurityin.us-cert.gov/bsi-rules/home/g1/771-BSI.html
+ *
+ * Some platforms (e.g. Windows) may provide their own version of this
+ * function.
+ */
+void smemclr(void *b, size_t n) {
+    volatile char *vp;
+
+    if (b && n > 0) {
+        /*
+         * Zero out the memory.
+         */
+        memset(b, 0, n);
+
+        /*
+         * Perform a volatile access to the object, forcing the
+         * compiler to admit that the previous memset was important.
+         *
+         * This while loop should in practice run for zero iterations
+         * (since we know we just zeroed the object out), but in
+         * theory (as far as the compiler knows) it might range over
+         * the whole object. (If we had just written, say, '*vp =
+         * *vp;', a compiler could in principle have 'helpfully'
+         * optimised the memset into only zeroing out the first byte.
+         * This should be robust.)
+         */
+        vp = b;
+        while (*vp) vp++;
+    }
+}
+#endif
diff --git a/putty.h b/putty.h
index dcc80db57..b32b0fa1e 100644
--- a/putty.h
+++ b/putty.h
@@ -1291,6 +1291,7 @@ int filename_serialise(const Filename *f, void *data);
 Filename *filename_deserialise(void *data, int maxsize, int *used);
 char *get_username(void);	       /* return value needs freeing */
 char *get_random_data(int bytes);      /* used in cmdgen.c */
+void smemclr(void *b, size_t len);
 
 /*
  * Exports and imports from timing.c.
diff --git a/ssh.c b/ssh.c
index ef503bf52..1f1a26567 100644
--- a/ssh.c
+++ b/ssh.c
@@ -3849,7 +3849,7 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
 		ret = loadrsakey(s->keyfile, &s->key, passphrase,
 				 &error);
 		if (passphrase) {
-		    memset(passphrase, 0, strlen(passphrase));
+		    smemclr(passphrase, strlen(passphrase));
 		    sfree(passphrase);
 		}
 		if (ret == 1) {
@@ -6294,7 +6294,7 @@ static int do_ssh2_transport(Ssh ssh, void *vin, int inlen,
 	assert(ssh->csmac->len <=
 	       ssh->kex->hash->hlen * SSH2_MKKEY_ITERS);
 	ssh->csmac->setkey(ssh->cs_mac_ctx, keyspace);
-	memset(keyspace, 0, sizeof(keyspace));
+	smemclr(keyspace, sizeof(keyspace));
     }
 
     logeventf(ssh, "Initialised %.200s client->server encryption",
@@ -6360,7 +6360,7 @@ static int do_ssh2_transport(Ssh ssh, void *vin, int inlen,
 	assert(ssh->scmac->len <=
 	       ssh->kex->hash->hlen * SSH2_MKKEY_ITERS);
 	ssh->scmac->setkey(ssh->sc_mac_ctx, keyspace);
-	memset(keyspace, 0, sizeof(keyspace));
+	smemclr(keyspace, sizeof(keyspace));
     }
     logeventf(ssh, "Initialised %.200s server->client encryption",
 	      ssh->sccipher->text_name);
@@ -8151,7 +8151,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
 		    key = ssh2_load_userkey(s->keyfile, passphrase, &error);
 		    if (passphrase) {
 			/* burn the evidence */
-			memset(passphrase, 0, strlen(passphrase));
+			smemclr(passphrase, strlen(passphrase));
 			sfree(passphrase);
 		    }
 		    if (key == SSH2_WRONG_PASSPHRASE || key == NULL) {
@@ -8730,7 +8730,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
 			     */
 			    /* burn the evidence */
 			    free_prompts(s->cur_prompt);
-			    memset(s->password, 0, strlen(s->password));
+			    smemclr(s->password, strlen(s->password));
 			    sfree(s->password);
 			    ssh_disconnect(ssh, NULL, "Unable to authenticate",
 					   SSH2_DISCONNECT_AUTH_CANCELLED_BY_USER,
@@ -8746,7 +8746,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
 			 * re-enter it if they louse up the new password.)
 			 */
 			if (s->cur_prompt->prompts[0]->result[0]) {
-			    memset(s->password, 0, strlen(s->password));
+			    smemclr(s->password, strlen(s->password));
 				/* burn the evidence */
 			    sfree(s->password);
 			    s->password =
@@ -8813,7 +8813,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
 		 * We don't need the old password any more, in any
 		 * case. Burn the evidence.
 		 */
-		memset(s->password, 0, strlen(s->password));
+		smemclr(s->password, strlen(s->password));
 		sfree(s->password);
 
 	    } else {
diff --git a/sshaes.c b/sshaes.c
index 2800e021f..97935b7f1 100644
--- a/sshaes.c
+++ b/sshaes.c
@@ -1157,7 +1157,7 @@ void aes256_encrypt_pubkey(unsigned char *key, unsigned char *blk, int len)
     aes_setup(&ctx, 16, key, 32);
     memset(ctx.iv, 0, sizeof(ctx.iv));
     aes_encrypt_cbc(blk, len, &ctx);
-    memset(&ctx, 0, sizeof(ctx));
+    smemclr(&ctx, sizeof(ctx));
 }
 
 void aes256_decrypt_pubkey(unsigned char *key, unsigned char *blk, int len)
@@ -1166,7 +1166,7 @@ void aes256_decrypt_pubkey(unsigned char *key, unsigned char *blk, int len)
     aes_setup(&ctx, 16, key, 32);
     memset(ctx.iv, 0, sizeof(ctx.iv));
     aes_decrypt_cbc(blk, len, &ctx);
-    memset(&ctx, 0, sizeof(ctx));
+    smemclr(&ctx, sizeof(ctx));
 }
 
 static const struct ssh2_cipher ssh_aes128_ctr = {
diff --git a/ssharcf.c b/ssharcf.c
index 6bfbd8959..06f235c5b 100644
--- a/ssharcf.c
+++ b/ssharcf.c
@@ -75,7 +75,7 @@ static void arcfour_stir(ArcfourContext *ctx)
     unsigned char *junk = snewn(1536, unsigned char);
     memset(junk, 0, 1536);
     arcfour_block(ctx, junk, 1536);
-    memset(junk, 0, 1536);
+    smemclr(junk, 1536);
     sfree(junk);
 }
 
diff --git a/sshbn.c b/sshbn.c
index 484c423f0..999817db4 100644
--- a/sshbn.c
+++ b/sshbn.c
@@ -148,7 +148,7 @@ void freebn(Bignum b)
     /*
      * Burn the evidence, just in case.
      */
-    memset(b, 0, sizeof(b[0]) * (b[0] + 1));
+    smemclr(b, sizeof(b[0]) * (b[0] + 1));
     sfree(b);
 }
 
diff --git a/sshdes.c b/sshdes.c
index b12a91d51..03d2b3ae4 100644
--- a/sshdes.c
+++ b/sshdes.c
@@ -858,7 +858,7 @@ void des3_decrypt_pubkey(unsigned char *key, unsigned char *blk, int len)
     des_key_setup(GET_32BIT_MSB_FIRST(key),
 		  GET_32BIT_MSB_FIRST(key + 4), &ourkeys[2]);
     des_3cbc_decrypt(blk, len, ourkeys);
-    memset(ourkeys, 0, sizeof(ourkeys));
+    smemclr(ourkeys, sizeof(ourkeys));
 }
 
 void des3_encrypt_pubkey(unsigned char *key, unsigned char *blk, int len)
@@ -871,7 +871,7 @@ void des3_encrypt_pubkey(unsigned char *key, unsigned char *blk, int len)
     des_key_setup(GET_32BIT_MSB_FIRST(key),
 		  GET_32BIT_MSB_FIRST(key + 4), &ourkeys[2]);
     des_3cbc_encrypt(blk, len, ourkeys);
-    memset(ourkeys, 0, sizeof(ourkeys));
+    smemclr(ourkeys, sizeof(ourkeys));
 }
 
 void des3_decrypt_pubkey_ossh(unsigned char *key, unsigned char *iv,
@@ -887,7 +887,7 @@ void des3_decrypt_pubkey_ossh(unsigned char *key, unsigned char *iv,
     ourkeys[0].iv0 = GET_32BIT_MSB_FIRST(iv);
     ourkeys[0].iv1 = GET_32BIT_MSB_FIRST(iv+4);
     des_cbc3_decrypt(blk, len, ourkeys);
-    memset(ourkeys, 0, sizeof(ourkeys));
+    smemclr(ourkeys, sizeof(ourkeys));
 }
 
 void des3_encrypt_pubkey_ossh(unsigned char *key, unsigned char *iv,
@@ -903,7 +903,7 @@ void des3_encrypt_pubkey_ossh(unsigned char *key, unsigned char *iv,
     ourkeys[0].iv0 = GET_32BIT_MSB_FIRST(iv);
     ourkeys[0].iv1 = GET_32BIT_MSB_FIRST(iv+4);
     des_cbc3_encrypt(blk, len, ourkeys);
-    memset(ourkeys, 0, sizeof(ourkeys));
+    smemclr(ourkeys, sizeof(ourkeys));
 }
 
 static void des_keysetup_xdmauth(unsigned char *keydata, DESContext *dc)
diff --git a/sshdss.c b/sshdss.c
index 7c95d11b6..6cf5830d5 100644
--- a/sshdss.c
+++ b/sshdss.c
@@ -20,7 +20,7 @@ static void sha_mpint(SHA_State * s, Bignum b)
 	lenbuf[0] = bignum_byte(b, len);
 	SHA_Bytes(s, lenbuf, 1);
     }
-    memset(lenbuf, 0, sizeof(lenbuf));
+    smemclr(lenbuf, sizeof(lenbuf));
 }
 
 static void sha512_mpint(SHA512_State * s, Bignum b)
@@ -34,7 +34,7 @@ static void sha512_mpint(SHA512_State * s, Bignum b)
 	lenbuf[0] = bignum_byte(b, len);
 	SHA512_Bytes(s, lenbuf, 1);
     }
-    memset(lenbuf, 0, sizeof(lenbuf));
+    smemclr(lenbuf, sizeof(lenbuf));
 }
 
 static void getstring(char **data, int *datalen, char **p, int *length)
@@ -575,7 +575,7 @@ static unsigned char *dss_sign(void *key, char *data, int datalen, int *siglen)
     SHA512_Bytes(&ss, digest, sizeof(digest));
     SHA512_Final(&ss, digest512);
 
-    memset(&ss, 0, sizeof(ss));
+    smemclr(&ss, sizeof(ss));
 
     /*
      * Now convert the result into a bignum, and reduce it mod q.
@@ -584,7 +584,7 @@ static unsigned char *dss_sign(void *key, char *data, int datalen, int *siglen)
     k = bigmod(proto_k, dss->q);
     freebn(proto_k);
 
-    memset(digest512, 0, sizeof(digest512));
+    smemclr(digest512, sizeof(digest512));
 
     /*
      * Now we have k, so just go ahead and compute the signature.
diff --git a/sshmd5.c b/sshmd5.c
index 7112d4060..e5187a661 100644
--- a/sshmd5.c
+++ b/sshmd5.c
@@ -249,7 +249,7 @@ void hmacmd5_key(void *handle, void const *keyv, int len)
     MD5Init(&keys[1]);
     MD5Update(&keys[1], foo, 64);
 
-    memset(foo, 0, 64);		       /* burn the evidence */
+    smemclr(foo, 64);		       /* burn the evidence */
 }
 
 static void hmacmd5_key_16(void *handle, unsigned char *key)
diff --git a/sshpubk.c b/sshpubk.c
index 88ff17921..c29d8a58a 100644
--- a/sshpubk.c
+++ b/sshpubk.c
@@ -108,7 +108,7 @@ static int loadrsakey_main(FILE * fp, struct RSAKey *key, int pub_only,
 	MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
 	MD5Final(keybuf, &md5c);
 	des3_decrypt_pubkey(keybuf, buf + i, (len - i + 7) & ~7);
-	memset(keybuf, 0, sizeof(keybuf));	/* burn the evidence */
+	smemclr(keybuf, sizeof(keybuf));	/* burn the evidence */
     }
 
     /*
@@ -150,7 +150,7 @@ static int loadrsakey_main(FILE * fp, struct RSAKey *key, int pub_only,
 	ret = 1;
 
   end:
-    memset(buf, 0, sizeof(buf));       /* burn the evidence */
+    smemclr(buf, sizeof(buf));       /* burn the evidence */
     return ret;
 }
 
@@ -358,7 +358,7 @@ int saversakey(const Filename *filename, struct RSAKey *key, char *passphrase)
 	MD5Update(&md5c, (unsigned char *)passphrase, strlen(passphrase));
 	MD5Final(keybuf, &md5c);
 	des3_encrypt_pubkey(keybuf, estart, p - estart);
-	memset(keybuf, 0, sizeof(keybuf));	/* burn the evidence */
+	smemclr(keybuf, sizeof(keybuf));	/* burn the evidence */
     }
 
     /*
@@ -794,14 +794,14 @@ struct ssh2_userkey *ssh2_load_userkey(const Filename *filename,
 
 	    hmac_sha1_simple(mackey, 20, macdata, maclen, binary);
 
-	    memset(mackey, 0, sizeof(mackey));
-	    memset(&s, 0, sizeof(s));
+	    smemclr(mackey, sizeof(mackey));
+	    smemclr(&s, sizeof(s));
 	} else {
 	    SHA_Simple(macdata, maclen, binary);
 	}
 
 	if (free_macdata) {
-	    memset(macdata, 0, maclen);
+	    smemclr(macdata, maclen);
 	    sfree(macdata);
 	}
 
@@ -1116,10 +1116,10 @@ int ssh2_save_userkey(const Filename *filename, struct ssh2_userkey *key,
 	    SHA_Bytes(&s, passphrase, strlen(passphrase));
 	SHA_Final(&s, mackey);
 	hmac_sha1_simple(mackey, 20, macdata, maclen, priv_mac);
-	memset(macdata, 0, maclen);
+	smemclr(macdata, maclen);
 	sfree(macdata);
-	memset(mackey, 0, sizeof(mackey));
-	memset(&s, 0, sizeof(s));
+	smemclr(mackey, sizeof(mackey));
+	smemclr(&s, sizeof(s));
     }
 
     if (passphrase) {
@@ -1139,8 +1139,8 @@ int ssh2_save_userkey(const Filename *filename, struct ssh2_userkey *key,
 	aes256_encrypt_pubkey(key, priv_blob_encrypted,
 			      priv_encrypted_len);
 
-	memset(key, 0, sizeof(key));
-	memset(&s, 0, sizeof(s));
+	smemclr(key, sizeof(key));
+	smemclr(&s, sizeof(s));
     }
 
     fp = f_open(filename, "w", TRUE);
@@ -1160,7 +1160,7 @@ int ssh2_save_userkey(const Filename *filename, struct ssh2_userkey *key,
     fclose(fp);
 
     sfree(pub_blob);
-    memset(priv_blob, 0, priv_blob_len);
+    smemclr(priv_blob, priv_blob_len);
     sfree(priv_blob);
     sfree(priv_blob_encrypted);
     return 1;
diff --git a/sshrsa.c b/sshrsa.c
index 0c1b2ef5a..77a6bb250 100644
--- a/sshrsa.c
+++ b/sshrsa.c
@@ -110,7 +110,7 @@ static void sha512_mpint(SHA512_State * s, Bignum b)
 	lenbuf[0] = bignum_byte(b, len);
 	SHA512_Bytes(s, lenbuf, 1);
     }
-    memset(lenbuf, 0, sizeof(lenbuf));
+    smemclr(lenbuf, sizeof(lenbuf));
 }
 
 /*
diff --git a/sshsha.c b/sshsha.c
index cbe9d78b4..30113511b 100644
--- a/sshsha.c
+++ b/sshsha.c
@@ -253,7 +253,7 @@ static void sha1_key_internal(void *handle, unsigned char *key, int len)
     SHA_Init(&keys[1]);
     SHA_Bytes(&keys[1], foo, 64);
 
-    memset(foo, 0, 64);		       /* burn the evidence */
+    smemclr(foo, 64);		       /* burn the evidence */
 }
 
 static void sha1_key(void *handle, unsigned char *key)
diff --git a/unix/gtkwin.c b/unix/gtkwin.c
index 03f285515..241aa6bcd 100644
--- a/unix/gtkwin.c
+++ b/unix/gtkwin.c
@@ -3582,7 +3582,7 @@ int pt_main(int argc, char **argv)
     if (argc > 1 && !strncmp(argv[1], "---", 3)) {
 	read_dupsession_data(inst, inst->conf, argv[1]);
 	/* Splatter this argument so it doesn't clutter a ps listing */
-	memset(argv[1], 0, strlen(argv[1]));
+	smemclr(argv[1], strlen(argv[1]));
     } else {
 	/* By default, we bring up the config dialog, rather than launching
 	 * a session. This gets set to TRUE if something happens to change
diff --git a/windows/winmisc.c b/windows/winmisc.c
index f54e8a4d6..2166f4530 100644
--- a/windows/winmisc.c
+++ b/windows/winmisc.c
@@ -68,6 +68,14 @@ Filename *filename_deserialise(void *vdata, int maxsize, int *used)
     return filename_from_str(data);
 }
 
+/*
+ * Windows implementation of smemclr (see misc.c) using SecureZeroMemory.
+ */
+void smemclr(void *b, size_t n) {
+    if (b && n > 0)
+        SecureZeroMemory(b, n);
+}
+
 char *get_username(void)
 {
     DWORD namelen;
diff --git a/windows/winpgen.c b/windows/winpgen.c
index c83d0d20c..ffbeb1a4e 100644
--- a/windows/winpgen.c
+++ b/windows/winpgen.c
@@ -958,7 +958,7 @@ static int CALLBACK MainDlgProc(HWND hwnd, UINT msg,
 		 * Seed the entropy pool
 		 */
 		random_add_heavynoise(state->entropy, state->entropy_size);
-		memset(state->entropy, 0, state->entropy_size);
+		smemclr(state->entropy, state->entropy_size);
 		sfree(state->entropy);
 		state->collecting_entropy = FALSE;
 
diff --git a/windows/winpgnt.c b/windows/winpgnt.c
index 291593e49..21a69cc00 100644
--- a/windows/winpgnt.c
+++ b/windows/winpgnt.c
@@ -174,7 +174,7 @@ static void forget_passphrases(void)
 {
     while (count234(passphrases) > 0) {
 	char *pp = index234(passphrases, 0);
-	memset(pp, 0, strlen(pp));
+	smemclr(pp, strlen(pp));
 	delpos234(passphrases, 0);
 	free(pp);
     }
@@ -968,7 +968,7 @@ static void answer_msg(void *msg)
 	    MD5Init(&md5c);
 	    MD5Update(&md5c, response_source, 48);
 	    MD5Final(response_md5, &md5c);
-	    memset(response_source, 0, 48);	/* burn the evidence */
+	    smemclr(response_source, 48);	/* burn the evidence */
 	    freebn(response);	       /* and that evidence */
 	    freebn(challenge);	       /* yes, and that evidence */
 	    freebn(reqkey.exponent);   /* and free some memory ... */
diff --git a/windows/winstuff.h b/windows/winstuff.h
index df59631c4..d81515dc7 100644
--- a/windows/winstuff.h
+++ b/windows/winstuff.h
@@ -75,6 +75,8 @@ struct FontSpec *fontspec_new(const char *name,
 #define BOXRESULT (DLGWINDOWEXTRA + sizeof(LONG_PTR))
 #define DF_END 0x0001
 
+#define PLATFORM_HAS_SMEMCLR /* inhibit cross-platform one in misc.c */
+
 /*
  * Dynamically linked functions. These come in two flavours:
  *
diff --git a/x11fwd.c b/x11fwd.c
index 5b4f76cdc..1e04f542b 100644
--- a/x11fwd.c
+++ b/x11fwd.c
@@ -264,10 +264,10 @@ void x11_free_display(struct X11Display *disp)
     sfree(disp->hostname);
     sfree(disp->unixsocketpath);
     if (disp->localauthdata)
-	memset(disp->localauthdata, 0, disp->localauthdatalen);
+	smemclr(disp->localauthdata, disp->localauthdatalen);
     sfree(disp->localauthdata);
     if (disp->remoteauthdata)
-	memset(disp->remoteauthdata, 0, disp->remoteauthdatalen);
+	smemclr(disp->remoteauthdata, disp->remoteauthdatalen);
     sfree(disp->remoteauthdata);
     sfree(disp->remoteauthprotoname);
     sfree(disp->remoteauthdatastring);
@@ -487,7 +487,7 @@ void x11_get_auth_from_authfile(struct X11Display *disp,
 
     done:
     fclose(authfp);
-    memset(buf, 0, 65537 * 4);
+    smemclr(buf, 65537 * 4);
     sfree(buf);
     sfree(ourhostname);
 }