Help: Why avast find 'VBS:Malware-gen' always?

My Avast warning ‘VBS:Malware-gen’ when I open webs always, virus type :worm .VPS version :080426-0, 2008-04-26. I deleted it ,bug it will find in next web. Boot Scan don’t find virus.
My Avast version is Pro 4.8.1169.
Please help me resolve the problem,thanks!

Is the address of this malware (can be found in ‘Virus found’ avast! dialog) your local drive or some remote (http://…)? And in the remote case this malware address is the same for every web page or different for different pages?

I suggest:

  1. Disable System Restore and reenable it after step 3.
  2. Clean your temporary files.
  3. Schedule a boot time scanning with avast with archive scanning turned on.
  4. Use SUPERantispyware and/or Spyware Terminator to scan for spywares and trojans. If any infection is detected, better and safer is send the file to Quarantine than to simple delete than.
  5. Test your machine with anti-rootkit applications. I suggest avast! antirootkit or Trend Micro RootkitBuster.
  6. Make a HijackThis log to post here or, better, submit the RunScanner log to to on-line analysis.
  7. Immunize your system with SpywareBlaster or Windows Advanced Care.
  8. Check if you have insecure applications with Secunia Software Inspector.