Are you just talking about Firefox or in general. I suppose the short answer is ther is an arms race between the good guys and the bad guys. Criminal Hackers find and exploit any weakness they can see or create, and software developers try to fix and prevent the exploits. Developers make changes and improvements and hackers may be able then to discover new exploits. With Firefox some problems may relate to use of third party software or specific website configurations or actions. This is however not a topic within the discussion scope of this forum you should find some security related site to discuss this. * This site may be of some interest but is probably overly technical <br /> http://www.blackhat.com/ * This lists Firefox fixes https://www.mozilla.org/security/known-vulnerabilities/firefox.html * And USA government advice ** ''Why is Cyber Security a Problem?'' http://www.us-cert.gov/ncas/tips/ST04-001 ** ''Understanding Patches'' http://www.us-cert.gov/ncas/tips/ST04-006