Symantec/Norton offers a screening and removal tool for the April Fool’s virus tool.
This malicious software is also known as the Conficker virus or Downadup virus.
If you go to the Symantec site
You can run a scan on your system which will detect the virus if it is on your system.
This is currently known as the Symantec W32.Downadup Removal Tool 1.1.02 and it appears to be perfectly safe to run this on an XP or Vista system.
Unfortunately, one indication that this virus is active on your system is that it may prevent you from connecting to many security sites. If this happens, you will need to connect to the security page via an uninfected system and follow instructions to download the tool and run it on an infected system.