Yesterday I was surfing the Web and was knocked off by Windows Defender. I run Defender with Ad Aware free. A Defender window showed I was infected by five viruses, one of which was of the Win32 variety. I clicked the button to remedy the problem, which downloaded the file in the title. I scanned it with Ad Aware and got nothing, but Defender labeled the file as suspicious, which I thought was odd--so I did not run the file.

Instead, I downloaded and ran the Win prevalent malware removal tool and did a full scan. Result: 0 files infected. I downloaded and performed a smart scan with Win virus detection tool. Results again 0.

What's going on? Is the scandsys file legit or is it the virus? Are MS tools reliable? Is there an available 100% reliable online tool to check my pc for viruses? I was browsing on Firefox at the time. Defender has never behaved like this before.