When you scroll down a long page does the browser sometimes skip over a section? If it does then you might well have an infected computer. However *I suspect* this warning could well be a false positive that AVG seems prone to.
Do you have any browser add-on toolbars installed - if so does the warning go away if you uninstall them?
If the warning persists you could try clearing your browser cache, then restart the computer in safe mode and do a full system scan with your antivirus program; does it find anything? If not and you restart normally does it reappear?
David
