Very large file in C:\Windows\Temp\_avast_

This file is almost 4GB in size. I don’t think its malicious but I was wondering if deleting it would do anything bad to my computer. The extension of the file is .dat. Does anyone have any information about the file or if its needed by avast in anyway?

Do you currently have an on-demand scan running?

C:\Windows\Temp_avast_ is the location where avast! unpacks the files while it is doing a scan.

If you are not, feel free to delete it.

It will recreate itself soon enough.

On successful completion of the scan (e.g. no alert) the file should have been removed from that location. Generally the only file you would see in there would be the Webshlock.txt, which is used by the Web Shield.

What other security based applications do you have installed (anti-spy/malware, etc.) as that may have prevented avast from removing it after the scan ?

I did have an scan running the day before. I was running CCleaner and I notice the very large file. Ccleaner said it was a temp file but it couldn’t delete it.

I have Avast, Malwarebytes and Comodo firewall installed. The only one I can think of, that might have prevented Avast from removing the file is Comodo firewall. But this has never happened before so I’m not 100% sure if it could have been Comodo firewall.

There is a possibility that it is just a one off hiccup.

Whilst MBAM shouldn’t be an issue unless you have the Pro version that has resident protection. If you have the pro version, you could exclude the C:\Windows\Temp_avast_ folder in the MBAM Ignore List.

If you only have the comodo firewall installed and not the anti-virus element also, it shouldn’t be that. I don’t know if the Defence+ element of comodo is active and how that may interact.

For now I would just monitor this and see if it happens again.

In order to delete objects remaining in the avast folder you would probably need to disable the avast self-defence module - avastUI > Settings > Troubleshooting.

Seems like the file is gone now. I ran CCleaner today and it no longer shows 4Gb in temp files. I went to C:\Windows\Temp_avast_ and the file is no longer in there. Seems like it took Avast a bit of time to remove the file but now it’s fully gone. Like you said, it was a “one off hiccup”. Thanks for all the help. Problem is fully resolved now.

You’re welcome.