Find any viruses, also what do you use to protect your system against spyware/malware.
If the answer to the second part is nothing, get Ad-aware and Spybot Search & Destroy - they'e both free programmes. Also download Ewido from www.ewido.net/en it's only a 14 day shareware programme, but if you run it right away and delete anthing it finds.
Keep all your spyware/malware and anti-virus programmes updated and run them all on a regular basis (I find that once a week at least is best), you will get around that long lag time.
I use windows (home) XP system with SP2.Run an anti virus program (Avast 4.6) about two-three times a month. Use to take about 140 min looking thru 304000 files. Ran it today, took 270 min (41/2hrs) and looked thru 515140 files. It has been upgraded several times since I last ran it, however for something to take 41/2 hours seems a bit long. Just a home PC, not that many songs or data on it. Can any body guess why so long?