For further information on all CSB (Collective Security Bulletin) issues, please read the related advisory TYPO3-SA-2010-015 that was published today:
http://typo3.org/teams/security/security-bulletins/typo3-sa-2010-015/
In general the TYPO3 Security Team recommends to read the following pages:
The TYPO3 Security Cookbook:
http://typo3.org/fileadmin/security-team/typo3_security_cookbook_v-0.5.pdf
Make sure you are subscribed to the TYPO3 Announce List:
http://lists.typo3.org/cgi-bin/mailman/listinfo/typo3-announce
See all TYPO3 security advisories:
http://typo3.org/teams/security/security-bulletins/