F-secure has an excellent write-up on their blog that details an impending Sober attack, scheduled for January 06, 2006:

Sober.Y was the biggest email outbreak of the year. It still is responsbile for around 40% of all the infections we see. This variant is programmed to activate on January 6th, 2006. After this date all the infected machines will regularily try to download and run a file from a website, forever. The virus even synchronizes the machines via atom clocks so the activation will not happen before January 6th, even if the clock of the computer is incorrect.

Scan early, scan often. But the more interesting part of their log entry is this:

The Sober virus author can precalculate the URLs. We wanted to be able to do the same thing. So we cracked the algorithm. This enabled us to calculate the download URLs for any future date. In fact, we did this already in May 2005, and we informed the local police in Germany as well as the affected ISPs. But we didn’t want to talk about it publically then – we didn’t want to fill in the virus writer on this. But he must know this by now.

And then they give examples of the URLs. Nice work.