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In uBlock Origin ("uBO"), strict blocking is the blocking of a whole page, i.e. the root document is blocked, so that not a single connection is made to the remote server hosting the web page.
By default, strict blocking is enabled in uBO (this is the opposite of Adblock Plus).
Adblock Plus only blocks secondary resources (see web pages themselves are never filtered).
So if you were to create a filter such as
||example.com^, and then navigate to https://example.com, Adblock Plus would not prevent you from connecting and loading the web page itself served at
https://example.com, though all secondary resources pulled by that web page would be subject to filtering.
uBO respected that semantic until version 0.9.3.0. With version 0.9.3.0, uBO will subject web pages themselves to filtering.
This means that using the same test case above, uBO will block the web page served by a server found in one of the malware list (unlike Adblock Plus):
Why the change? Because issue #1013 brought forth why it is desirable sometimes to completely block a web site, as opposed to what the ABP-filtering semantic dictates.
In the end, the chosen solution is to now have web page themselves subject to filtering, just like all secondary resources.
In the figure above, the user will be given the choice to go back by closing the window or proceed to the web page by disabling strict blocking by selecting either:
- Temporarily - The site will be temporarily allowed for a limited time (currently set at 60 seconds).
- Permanently - The site will be permanently allowed.
This will prevent the web page proper for the site from being blocked by uBO in the future: the filtering of the site will be done exactly as per ABP-filtering semantic, and just like with uBO pre-0.9.3.0.
There are many benefits to strict blocking. For example, there is no good reason one should want to connect at all to any of the sites present in any one of the malware domain lists. Strict blocking will prevent this from happening.
Important note: Keep in mind that when the above warning occurs, it doesn't necessarily mean the site is harmful, it just means that there is a matching filter in the selected filter lists. You decide whether the site is safe, and whether disabling strict blocking permanently for the site is appropriate.
Tip: If you wish, you may entirely disable strict blocking everywhere by adding the rule
no-strict-blocking: * true to the My rules pane in the dashboard (don't forget to click Commit to make the rule stick).