I have noticed that scanning a single file will produce results that say the total size of the file scanned is much larger than the actual file size listed in file properties, and I don’t mean with zipped files. Why this is?
Well, are you sure that avast! doesn’t recognize the file as an archive, extracting its content?
What does the “number of scanned files” show? One, or something bigger?
Besides what Igor said, can you give some examples of the file names were you see this ?
The file size on the properties if I’m not wrong doesn’t include any alternate data streams (ADS) that are part of the file. I don’t know if avast by default would scan these ADS but if so would also be included in the total size scanned.
Microsoft word .docs are another anomaly see image example where this .doc file is reported as 22KB, but 40.7KB (and 6 files), so avast reports what it actually gets from that file not the raw info from file properties/explorer.