Full scan has shown much more files than my computer should have after update

[REDACTED]

This has been with my Avast from the last summer. I remember it first occuring after I returned from summer vacation trip and my computer notified me about Avast update to newer version, though I don't remember which version it was, but I've upgraded Avast twice into newer version after that with the newest being Avast 2016.11.1.2241. I didn't come up here earlier since I thought it had something to do with that when I got home from the trip, my Windows Update also performed updates, anong installing some files ready for Windows 10 I recall (I still haven't updated my Win 7 to 10 yet though).

The thing is that since that Avast program update, running full scan with Avast on my computer now has taken double of the time it took before (it used to take only about an hour, now it has taken two), and more interesting, scan results show that Avast has scanned files for over 600 Gb, when combined space that my pc's C:\ and D:\ drives take should be rounded 370 Gb (size of my whole drives' space combined should be well over 1000 gb). Also, during first half of a full scan (first one hour) scan process (that circle thing that shows how far scan is going, I don't know its name...) seems to be stuck showing 0% but Avast still seems to scan lots of files during that time and after first hour used on full scan the circle starts moving normally untill scan completes at 100%. The whole thing hasn't seemed to be a problem, other than scan itself takes twice more time than before.

I guess at least part of this can very well be about my computer having much more files than before and full scan has showed variable results since then with me cleaning up computer space etc. I haven't installed anything massive outside few games from Steam and Battle.net, system updates and new personal video & image files. I've noticed that my Steam folder alone takes at least one hour to scan. But still the fact that the full scan started showing more scanned gigabytes and taking much more time seem a bit odd to me. When I do individual Avast scan for my drivers they show the correct amount of bytes the disks should hold. Also individual scans for my C:\ drive has always took casually about two hours to do. I'm not sure if this is about newer Avast versions having some advanced full scan or just something with my Avast's settings, though I don't recall messing with full scan settings.

I've believed that this could've had been doing something with some Windows 10 preinstallation files being stored on my computer, but after doing a full scan with $Windows.~BT folder left out, the scan result hasn't shown significant difference. Could this whole thing have something to do with full scan settings/mechanics been changed/improved with newer version of Avast?

[DavidR]

Have you made any changes to the full system scan settings ?

Assuming that you haven't changed the default settings of the full system scan.

This isn't unusual as the data scanned against data on the drive aren't the same.

On your hard drive you will have many archive files, when you run a full scan those archives are unpacked and the contents scanned. So the data scanned will be much higher than the size of the archive file. But to be almost double is somewhat strange, that is way too much unless you have a huge amount of archive files.

As for the scan duration, given what you say about the size of data scanned being almost double that would also have an impact on scan duration.

With a new installation the persistent and transient caches would need to be repopulated, this could take a few scanned. You also need to take advantage of persistent cache, so you need to allow the avastUI > Scan > Scan for viruses > select your scan from the drop down list - Scan settings - 'Store data about scanned files in the persistent cache. You could also increase the scan priority.

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I checked my Avast full scan settings and noticed that I had set Heuristics Sensitivity to "High" at some point, and that "Speed up scanning by using the persistent cache" disabled, but I don't recall setting the latter myself.

[DavidR]

1. The "Speed up scanning by using the persistent cache" should be enabled by default, being off could slow scanning.

2. The 'Store data about scanned files in the persistent cache.' could improve scan speed if 1. above is enabled, the default setting is 'off' why they chose that as the default option I don't know. But initially it would cause a delay in scanning (how much I don't know) as it writes that data to the cache.

[REDACTED]

I ran a scan with "Speed up scanning by using the persistent cache" enabled. Scan took a bit shorter time than before, but the results still show over 600 Gb being scanned.

[DavidR]

The persistent scan may help with speed, but unfortunately that won't do anything for the data scanned.

I'm at a bit of a loss as to what (else) to do to check this - I just wonder if you have any large hidden folders that may not be recorded in the windows explorer calculations.

It might be worth running a temp files cleaner, such as CCleaner to see if that removes any dross.

[REDACTED]

Hello again! A little update for this, if it matters...

When I've scanned my C:\ drive I've done it by going to My computer folder and scanned it with Avast by right-clicking it. Yesterday I went and tried it trough Avast's Select folder to scan option. I noticed that the latter only takes one and half hour to complete where as with former it takes whole 2 hours, but they seem to show similar amaunt of scanned space. Is there any factors that would make Avast's Select option more fast than "go to folder -> right click -> scan with Avast"?

[DavidR]

The right click scan is one of the most thorough of scans, so I wouldn't recommend using it for other than specific files or small folders.

If you open the Folder Select scan and then go to the Scan settings you will see exactly what it scans as there are exceptions to what it scans. In the Right click scan as far as I'm aware there are no such exceptions and I don't know if it takes advantage of the persistent cache either.