Why is scanner X not in use?

Probably because there is no Linux version available. In some cases because the manufacturer does not allow the use of their scanner on web services like these.

My local copy of scanner X insists the file is infected, but here this same scanner says it is clean! How is this possible?

There can be several reasons for this discrepancy. The most frequent scenario: the scanner vendor fixed a false positive (an unwarranted virus detection) in a product update that your local scanner has not received yet, but we have. Also, occasionally a scanner may produce slightly different results due to engine differences across platforms (we use Linux products).

I submitted a file for scanning a short while ago, but I cannot find it on my computer any more. I need this file badly and I can prove I was the one to submit it. Can I get a copy?

Although this is often technically possible, we will not send it (back) to you. We have a strict policy: nothing that enters our virus pool will be distributed to entities outside the anti-virus/security industry. Sorry.

I think my computer is infected. Can you help me?

No. Contact your anti-virus vendor for assistance.