Mydoom.F - which was found a month ago - has been gaining ground over the last weeks. It's now in the the Top 10 of current virus threats. This virus also runs a sustained DDoS attack against the website of Recording Industy Association of America at www.riaa.com.
This site has been down since Wednesday. There is some speculation on whether this is caused by Mydoom.F or not.
The same worm also attacks www.microsoft.com, which is doing just fine.