TYPO3 is an open source PHP based web content management system released under the GNU GPL. TYPO3 is copyright © 1999-2020 by Kasper Skaarhoj.
Official Installation and Upgrade Guide
You can find instructions regarding installation and upgrade at https://docs.typo3.org/installation
Server system requirements
Find the official system requirements in TYPO3's documentation.
To ensure a secure installation, you have to make sure that you keep your TYPO3 core and the extensions up to date.
Subscribe to the announcement mailing list. This will inform you about new releases of the TYPO3 core and security bulletins of core and community extensions. http://lists.typo3.org/cgi-bin/mailman/listinfo/typo3-announce
Please refer to official TYPO3 Security Guide for further information about security-related topics of TYPO3 CMS and the resources compiled by the Security Team. https://docs.typo3.org/typo3cms/SecurityGuide/ https://typo3.org/teams/security/resources/
Please consider also hardening your TYPO3 instance further by adjusting permissions on non-changing files/folders.
TYPO3 Contribution Guide
You can find further information in the README.md.