We have received word from Brian Mastenbrook, who has discovered security vulnerabilities with Apple stuff in the past, that a severe vulnerability exists in the Safari browser. Brian says there is a possibility that a hacker can take control of any system that runs Safari due to a hole in the way Safari handles RSS feeds. Brian is not publishing specifics of the security hole to prevent exploitation but he has acknowledgement from Apple that the problem exists.
Mac users can simply change the Safari preferences to use another program to handle RSS feeds. Windows users who use Safari are not so lucky and it is suggested they use a different browser until Apple issues a fix for the problem.