malware alert!

ok first of all i have the mcafee 3 in one total protection insalled on my computer ive used them for years and never had any problems now i have this malware alert box that keeps popping up on line or off line it dosent matter ive run numerous scans and it comes up clean,but yet still have this security alert that pops up:confused. this is what the box reads word for word.................
warning!

trojan adware.w32.expdwnldr spyware detected. this trojan allows attackers to access your computer from remote locations,stealing passwords,internet banking and personal data.this also promts advertising popups this is a security risk and should be removed from your system.

type: trojan horse
system affected: windows 98,2000,nt4,me,xp
security risk (0-5): 4
recommendations: click 'yes' to get available antispyware software.


yes no


thats the hole message.i even have crapcleaner and that dosent help what do i kneed to do or get to help solve this problem?????and it has to be a free program i dont have n-e money right now...please help ill try any suggestions.

thanks