Virus or maleware?

Hi all
Since last week I'm having big trouble with my laptop.
I'm running Spybot 1.4, spywareblaster and Symantex Antivirus corporate edition.
Never had a problem before + I'm updating them daily.

Any way, I don't know what's happened, but spybot is not there any more.
If I install it again and I click on the desktop icon just after the installation it says "file not found" and this is confirmed by the missing executable in the program files/spybot directory.
Same problem with the antivirus, is not working any more. So I've removed symantec and installed f-prot. Same problem... every time I click on the tray icon it starts the installation from scratch :-(
Same music with other antivirus.

It seems to me a nasty virus.
I've used different antivirus from a bootable USB key and they don't find anything.

The system boots up correctly but windows XP is pretty slow now

I was just wondering if anybody have run into this same problem

Thanks to read!
rs232

There is malware that appears to remove Spybot's executables and some that disables anti-virus software. Consider posting in the Malware Removal forum and having someone take a look at your system. Follow the instructions here:

• "BEFORE you POST" Mandatory Steps Before Requesting Assistance.
  http://forums.spybot.info/showthread.php?t=288

After completing those steps, start a new thread (topic) in the following forum (making sure to include the HijackThis log and online scan logs produced from the instructions above):

• Malware Removal
  http://forums.spybot.info/forumdisplay.php?f=22