If a virus is replicant (coming and coming again), you should:

  1. Disable System Restore on Windows XP: http://support.microsoft.com/default.aspx?scid=kb;[LN];310405
  2. Clean your temporary files.
  3. Schedule a boot time scanning with avast. Start avast! > Right click the skin > Schedule a boot-time scanning. Select for scanning archives. Boot.
  4. Besides ewido, try a-squared or Spyware Terminator (trojan removers).

Other option is scanning in SafeMode (repeatedly press F8 while booting): http://support.microsoft.com/default.aspx?scid=kb;en-us;315222