avast! Free "Shields" are corrupting downloads

[Satsujinlol]

So the last week has been very hectic for me due to some strange file corruptions that would happen while downloading a file (including cache files), that made YouTube videos, SoundCloud tracks, etc. would stop loading after a short period.
I first thought this was an issue with the flash player or firefox, but it happened while downloading files as well!

The download process would start, go on for a varied period of time, then finish in the middle of the downloading process. I read that a file being corrupted would do this, but since all of the files I downloaded did this, it had to be something on my side that corrupted the files.
My first assumption was that this must have been caused by a malware that has somehow gotten past my antivirus, so I performed a scan which turned out clean.

After pondering about the issue, something crossed my mind; avast! is searching all the files I download for malware!
I tried turning off the shields, and it jolly well indeed worked!

Conclusion:
Somehow during the scan, avast! is corrupting the files I download with some peculiar scan for malware, leaving me with unfinished files, including the videos stored in the cache.

I now need to switch off my shields in order to download a file or watch a video on YouTube. I am sure this is not intended, and should be fixed.

I use:
Intel i7 2600K 3.40GHz
8GB RAM
NVIDIA GeForce GTX 560
Windows 7 Home Premium 64-bit (6.1, Build 7601)

avast! Free:
Virus definition version - 120119-1
Program version - 6.0.1367

[ady4um]

Any specific information about the site or files that are being blocked / corrupted? Any message, screenshot, chest, log, report,... ?

[daimaah]

You're not alone, I have noticed this as well. First I blamed the server (f.ex. when downloading Left 4 Dead 2 maps from l4dmaps) but turns out it was Avast all along. Also corrupts League of Legends patch installations etc. It's quite frustrating to disable shields any time I need to download anything. uTorrent downloads files without issues however.

[Montmorency]

When trying to download LastPass .exe installer (from LastPass's site and from Softpedia) both File Shield and Web Shield reported it as Trojan Dropper and quarantined them.
What's going on?
Some months ago I had to give up on the Behaviour Shield because it would block a lot of legitim files and now this?

[CraigB]

Some months ago I had to give up on the Behaviour Shield because it would block a lot of legitim files and now this?

You only have to tell the behaviour shield that the process is trusted and add it to the list then you wont be asked again.

Also with your lastpass file you can run a check scan with virus total to make sure it's not infected, if all's good then report the false detection to avast.

[ady4um]

I don't know the exact reasons to block. Avast Team may need to look into this so to evaluate if this is a FP or whatever else.

In the meantime, as a workaround, I would suggest setting the relevant shields with "EXPERT" settings -> actions -> "ask" where pertinent / relevant. This should give you the possibility / opportunity to decide what to do, instead of avast acting by default.

[Montmorency]

Some months ago I had to give up on the Behaviour Shield because it would block a lot of legitim files and now this?

You only have to tell the behaviour shield that the process is trusted and add it to the list then you wont be asked again.

I would if I had been given a warning; but it would just block. It took me the best part of two days to find the culprit.

[Satsujinlol]

Any specific information about the site or files that are being blocked / corrupted? Any message, screenshot, chest, log, report,... ?

I'm sorry for the slow response, but every site is being blocked. A download would start normally, but it would stop after a while no matter where I downloaded it from, I say.
I haven't found any sort of indication like a log or a report that it is getting blocked. All I know is that if I turn the shields off, my downloads doesn't suffer these symptoms.

EDIT: My laptop has started getting the same errors. I'm starting to think this is quite an error I've found here.

[Gargamel360]

Any specific information about the site or files that are being blocked / corrupted? Any message, screenshot, chest, log, report,... ?

I'm sorry for the slow response, but every site is being blocked. A download would start normally, but it would stop after a while no matter where I downloaded it from, I say.

What he means is, he wants a specific link to a download (and a safe one at that) that has failed for you so we can try to see if we also have the same problem.  

[ady4um]

Do you use any download manager of any kind?

In addition...

First, set ON all shields.

Then, please delete the firewall rules related to avast (from whichever firewall you have, disabled or enabled, third party one, Windows firewall, or from avast firewall, hardware firewall... from all of them), save and reboot. The firewall rules will be re-created where necessary after the reboot ("learning mode" or equivalent).

Test, reboot AGAIN, test again, and report back.

[Satsujinlol]

Do you use any download manager of any kind?

I'm using Firefox' built-in downloader.
As I said, it basically stops everything I download. Including buffering YouTube videos, SoundCloud tracks, and other files buffered through flash. I've tried using FlashGot, but it stops those too.


On the laptop, I use a proxy to connect to the internet. Somehow avast! shields are blocking that, too... and I have to go through that proxy to get online.

What he means is, he wants a specific link to a download (and a safe one at that) that has failed for you so we can try to see if we also have the same problem.  

1. Go to YouTube frontpage.
2. Click on a video.
3. Does it load correctly?

First, set ON all shields.

Then, please delete the firewall rules related to avast (from whichever firewall you have, disabled or enabled, third party one, Windows firewall, or from avast firewall, hardware firewall... from all of them), save and reboot. The firewall rules will be re-created where necessary after the reboot ("learning mode" or equivalent).

Test, reboot AGAIN, test again, and report back.

I will do this when I get home (4 hours). I don't have access to the Windows firewall on the laptop.

EDIT: There aren't any settings in the Windows firewall that mentions avast! and rebooting seems to suppress it the issue for a while.

[ady4um]

Have you configured avast -> settings -> updates -> proxy settings?

In addition, since when this is happening? Was there any change / update / (un)installation? Or was this right since the first time you installed avast?

Which security tools you had before avast? And now, besides avast?

Does the router have any firewall?

Something (probably old or bad firewall rule) is blocking access to avastsvc, so nothing will get connected. Some remnant of some other security tool may be conflicting too (in which case, there is a need to run the adequate removal utility).

What do you mean with:

rebooting seems to suppress it the issue for a while

?

[Satsujinlol]

Have you configured avast -> settings -> updates -> proxy settings?

I'll do that on my laptop :>
My desktop doesn't need any proxies, and I can connect to the update server.

In addition, since when this is happening? Was there any change / update / (un)installation? Or was this right since the first time you installed avast?

This started about a week ago. I've been using avast! for 4-5 years and the issue probably came with the latest update. My client updates automatically, and silent/gaming mode is active so I don't know when the update came.

Which security tools you had before avast? And now, besides avast?

I'm using Malwarebytes Anti-Malware for scanning the computer, and I use Toolwiz Care for maintenance. The Windows firewall is ofc on.

Does the router have any firewall?

I don't have access to the router, and I assume yes. No recent changes there.

Something (probably old or bad firewall rule) is blocking access to avastsvc, so nothing will get connected. Some remnant of some other security tool may be conflicting too (in which case, there is a need to run the adequate removal utility).

avast! can indeed connect to the update server, so the firewall isn't blocking it completely in that case. I'm quite sure the issue isn't there but rather in the software itself.

What do you mean with:

rebooting seems to suppress it the issue for a while

?

After rebooting I can watch videos and such for about 20min or so, then it would start being all derpy. The issue is in the cache maybe?

[ady4um]

My client updates automatically, and silent/gaming mode is active so I don't know when the update came.

Do you mean *definitions* autoupdates, or also the *program* itself?

We have seen firewall issues several times after a program update for avast is performed, even when it seems that the firewall rule is correct. So deleting the relevant rules and re-creating them usually solves this type of problems.

But your case seems to be different (at least partially), since you are able to connect (for at least a period of time).

Maybe you could try disabling "game mode" in avast for some time, so at least you would be able to see any potential messages? (BTW, do you have the Status Bar options enabled and the pop ups settings too?).

I don't see (until now at least) something in avast that would block a download after some period of time. I mean, either it blocks it, or it doesn't.

You may want to try uninstalling multimedia related tools. For example, uninstall all from adobe (like "flash" and "macromedia shockwave" for example), and be sure to uninstall all versions of them. Then reboot and install the latest stable versions.

I would do the same with JAVA (which can install more than one version in parallel, and they are left behind if you don;t uninstall them manually). JavaRa may be useful for this. So finally you would use only the latest stable JAVA version available.

After rebooting, I would try also updating your web browser, if the problem still presents itself.

Or maybe you should uninstall avast, run the removal utility (several times, each for each version of avast you ever had) and install the latest stable (and reboot) http://www.avast.com/uninstall-utility.

Maybe someone else has some additional tip / clue / idea.

[Satsujinlol]

Do you mean *definitions* autoupdates, or also the *program* itself?

Both, I believe.

Maybe you could try disabling "game mode" in avast for some time, so at least you would be able to see any potential messages? (BTW, do you have the Status Bar options enabled and the pop ups settings too?).

I will try disabling gaming mode. Not sure which status bar/pop-up settings you are referring to

I don't see (until now at least) something in avast that would block a download after some period of time. I mean, either it blocks it, or it doesn't.

I know, right? My theory is that the search process somehow corrupts the files when it's finished, or it "pulls" the file out prematurely for scanning.

You may want to try uninstalling multimedia related tools. For example, uninstall all from adobe (like "flash" and "macromedia shockwave" for example), and be sure to uninstall all versions of them. Then reboot and install the latest stable versions.

I would do the same with JAVA (which can install more than one version in parallel, and they are left behind if you don;t uninstall them manually). JavaRa may be useful for this. So finally you would use only the latest stable JAVA version available.

After rebooting, I would try also updating your web browser, if the problem still presents itself.

That were my thoughts exactly as I discovered the problem. So I updated to JRE 7, Uninstalled and re-installed Flash player (both 32-bit and 64-bit), hell, I even updated to Firefox' Nightly build 12!

Or maybe you should uninstall avast, run the removal utility (several times, each for each version of avast you ever had) and install the latest stable (and reboot) http://www.avast.com/uninstall-utility.

Maybe someone else has some additional tip / clue / idea.

I already tried re-installing avast! but as I said, the issue were on my laptop as well, so the issue is somewhere else...
I'm trying to find out what my desktop and laptop have in common, but I can't seem to find anything unique about them.