I have posted the paper on the security vulnerabilities found in Zone Alarm, Norton Antivirus and other programs. The paper is called "In Certificates We Trust" and it has all the juicy details about how changing the system clock could cause a great many programs to stop working even critical ones like anti-virus. With the vendors notified and the products fixed the fun was over for a while but it may be time to dust off this tidbit and see what it does now. Of course Microsoft was notified and said that it was not a security concern however in Vista they fixed this "non-issue" so does that mean it was really an issue?
At the time I created the paper the information was too sensitive to broadcast but now that Vista handily keeps you from changing system time via programs I think it's time to let people try this out on their old system just for fun to see if it works on any new programs.
The code and exe sample for the clock forwarding is here: http://www.trustsecurityconsulting.com/Downloads.html
There is a program to test the clock/certificate issue and another (if you are affected by this problem) to watch for and correct wild clock changes that cause the issues mentioned in the paper.