Users have been urged to upgrade to the latest versions of Mozilla"s software to protect themselves from a series of critical security holes. The Computer Emergency Readiness Team (CERT) warned on Monday that earlier versions of Firefox, and other Mozilla software based on Firefox code, contain a clutch of vulnerabilities that expose users to attack. The Mozilla Foundation released a new version of Firefox last week, version 1.5.0.2, which it said contained fixes for several security flaws.