Virus/Spyware in IE6?!?

I do desktop support for a couple of car dealerships. We use mcafee 8.5 and windows defender on all of the machines. When checking Mcafee OAS on several computers I am seeing 100s of files detected. Nothing shows up when you do a full virus scan. I have been experimenting with what may be causing this. It seems that when I browse the internet in using internet explorer for every link i click it adds an entry to Mcafee On Access Scan. Any Ideas as of what could be causing this? It only happens on computers running IE6. Our network is becoming very slow over the past 2 months and I am wondering if this may be the cause. Thanks ahead of time for any help you can give me on this.