SpyBot is great, I agree but I don't think it's the spyware problem
More probable that someone has hijacked your PC if you don't have a strong enough firewall and got your credit cards info stored inside ... wait a second!
Do you keep your CC info on your PC???
Rule #1: NEVER store your CC info on the PC (even encrypted).
Rule #2: Arm yourself with good firewall (MS Windows firewall is a joke).
I suggest both hardware (router) and software (ESET, Kaspersky, Zone Alarm Pro or Agnitum Outpost Pro).