If you recently installed Sophos AntiVirus software on your Apple computer, sorry: you probably need to remove it and install an updated version.
At UC Davis, the problem concerns anyone who:
1) downloaded Sophos for Macs from the campus software Web site between Jan. 16 and Jan. 21.
2) installed it from the fall 2008 campus Internet Tools CD on or after Jan. 16.
3) installed it before Jan. 16, but somehow has not accepted updates to the software. (Updates usually arrive automatically, but users can block them.)
Basically, if any of those conditions apply, the version on your Apple won't accept further updates, and without updates the anti-virus will lose its power to protect your machine and your data against worms, viruses, and other electronic vermin. You'll know the software isn't updating if you see a red "X" on top of the Sophos shield icon on your computer.
In any event, the fix is easy. Install the current version of Sophos AntiVirus here. The campus makes Sophos available for free to all faculty, students and staff.
The problem does not affect the current version of Sophos AntiVirus for PCs, which the campus has distributed since last summer. Nor will the problem affect earlier versions of Sophos AntiVirus for PCs, as long as you have continued to accept updates. (If you have version 7.1 or earlier and have refused updates, your version of Sophos AntiVirus for PCs no longer works effectively. You should remove it from your PC and replace it with the current version.)
Every other piece of software on the fall 2008 Internet Tools CD is still valid. Discard older versions of the CD, which are outdated.
A technical article about the Sophos situation is available here. For help, contact the IT Express Computing Services Help Desk at (530) 754-HELP (4357).