Hackers Can Root Macs by Going Back in Time
A bug in OS X 10.8 Mountain Lion and 10.7 Lion allows attackers to gain superuser access if they reset the clock to 1 January 1970. The bug shouldn’t affect most people, as the attacker also needs shell access to the Mac, and the user must have enabled superuser access in the past.
There is a partial workaround for this problem that I use. I edit the bash logout file .bash_logout to include this line:
sudo -K
(that's a capital K).
This will remove any past sudo shell access from your history and block this exploit but only when you logout from the shell. When using sudo for anything, I always create a new shell window in Terminal and exit when I'm done. This ensures that the logout script runs.
The best part is that if or when Apple fixes this, you don't really have to do anything because the only consequence to doing this is that you get the initial warning message each time you used sudo instead of just the first time.