underlig popup

Jeg bliver ved med at få en popup som skriver følgende:

Attention! System detected a potential hazard (TrojanSPM/LX) on your computer that may infect executable files. Your private information and PC safety is at risk. To get rid of unwanted spyware and keep your computer safe you need to update your current security software. Click yes to download official intrusion detection system (IDS software)

Hvordan får jeg lige det til at holde op?
-Jeg har forsøgt at installer ad-aware, men det kan jeg ikke fordi versionen af windows installer i windows 98 er for gammel...