A few month ago, Techspot spoke with AppRiver regarding the attack of the Storm worm earlier this year. Among other things, it was speculated that the initial attack was just a test run and that variants would soon follow. That is definitely happening, with a follow-up attacking occurring this week. In fact, according to another spam filtering company, Postini, yesterday marked the largest e-mail virus attack in a year:

The recent Storm Worm proliferation, coupled with a similar attack earlier this week that involved e-mails with "missile attacks" in the subject line, have made this the most active week for e-mail virus attacks in at least a year, according to Postini.
Most of the blame is being placed on two variants of the Storm Worm, and it is thought that these particular floods will result in many more downloads and, ultimately, infected machines.