Sober returns

I've received a large number of these today:

Dear Sir/Madam,

we have logged your IP-address on more than 30 illegal Websites.

Important:
Please answer our questions!
The list of questions are attached.

Yours faithfully,
Steven Allison

*** Federal Bureau of Investigation -FBI-
*** 935 Pennsylvania Avenue, NW, Room 3220
*** Washington, DC 20535
*** phone: (202) 324-3000

They've all contained a copy of the Sober.CF worm. I'm assuming I'm not the only one so please check to make sure your AV software is up to date.