I use the avast free antivirus ... and i sort of noticed a very strange occurrence. Whenever I scan a document from avast, the application scans more data then there is on the document. For e.g., if the document size is 1 GB, the scan results will show that the total data amount tested was around 3 GB. This really concerns me, is my computer virus infected or is this a normal thing.

closed as off-topic by tylerl, Xander, NULLZ, Ayrx, Scott Pack Jul 21 '13 at 3:33

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions about general computing hardware and software are off-topic here, but can be asked on Super User." – tylerl, NULLZ, Ayrx
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This doesn't sound like you have much to worry about, but we do lack a fair deal of information to be absolutely sure. For example, you didn't mention what type of documents appear to be reported as of bigger size than, I imagine, your file explorer reports? Either case, this could be attributed to either file compression, disk/folder compression (if on Windows), or a simple case of poor data size calculation within Avast! antivirus. It's really hard to pinpoint the problem without more information, but I can't see how that could be attributed to any kind of infection.

As for the other part, the USB flash drive reportedly infected with malware using one antivirus software, and failing to report any such issues with your copy of Avast!, again, we're not having information to what antivirus software you're referring to with the other laptop, or what exactly has it reported. But I have seen in the past USB pen drives pre-installed with utility tools on same or a separate partition, and using autorun.inf file to start the tools menu when inserting the drive in Windows computers. These files are reported as potentially unwanted applications (or similar wording) in some antivirus softwares. I've even seen such renown companies as Corsair having this issue (or better said, AV vendors having issues with reporting false positives) in one of their older Voyager series of USB drives.

Anyway, hope this helps, but you really ought to include all information you can get your hands on and add them to your question, to help us identify your problem better and possibly suggest solutions to them.

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