Okay, after I built my new PC with Windows 7 64-bit, I downloaded a temperature monitor called CoreTemp which turned out to be malware. How do I know this? Because my Avast anti-virus failed to download an update giving me the message "Last encountered error: Invalid file signature. Setup will terminate.". I checked the Avast forums and someone said Avast was having an issue and another said it was malware so I ran MalwareBytes and it found the CoreTemp malware and removed it or I think it did as i'm still getting the Avast update error. Do I still have some malware or does anyone have another idea on how to fix this?

Edit: Another strange thing I noticed is that CoreTemp forces my home search engine to be Yahoo despite removing CoreTemp and even telling CoreTemp not to make Yahoo my search engine home in the first place. Is there a setting to get rid of Yahoo as my home search?

That's really unlucky.

Well, it so happens that you run Avast which supports a boot scan. It scans your drive(s) before Windows have loaded and by that giving a chance to kill viruses that loads during a windows boot up.

I would definitely run it in case you have noticed any misbehaviour because of it. I'm not sure if the Avast update has anything to do with the virus though, it could be a coincidence.

A tips when you run boot scan, only choose your system drive because if you have multiple, large drives it will take a long time to finish.

When you choose boot-time scan, remember to pick high Heuristics sensitivity, scan for PUPs and unpack archive files.

http://www.filehippo.com/download_hijackthis/

but be careful...

I re-downloaded all of my GOGs, is it possible they're infected?
And how do I do a boot scan? Nevermind, found it.

From the foums i'm reading, it sound like a problem with Avast not being able to update. I'm running a non-boot scan as the boot-scan was so slow that i'm not sure it was even running, it seemed to be frozen so I skipped it. There's a way to manually download the anti-virus updates, after my scan i'm gonna try a manual update and see if that suggested fix works.
Any info on if my GOGs could be infected with malware?

You can add specific locations at the boot-time scan parameters. While it's obvious there could viruses where you put them but it's good to scan your system files at least so if your system is on the same drive as some games then only pick folders such as C:\Windows (and any application that takes up a lot of memory).

Nothing found on the non-boot scan, but doing a manual download and installation of virus database seems to have cleared up the problem with Avast.

I'd just go with MSE and not bather with Avast if you're having issues with it.

I trust Malwarebytes above all others myself. I also use Webroot's Spysweeper. Tried Avast long time ago and did not care for it,..same with AVG,..Norton etc.

If you download a file that you deem even remotely suspicious and is under 32mb, you can upload it to Virus Total which will check the file with all currently available commercial anti-virus programs for free. I use it all the time and value it a lot.

I guess so, though it was a good idea to ditch CoreTemp and get rid of its malware.

One more question though, does anyone have any idea of how to get rid of Yahoo as my home search page for Google Chrome? That's the one part left over from CoreTemp i'd like to quash.

Go to your Menu (Upper right corner) and choose Settings. One of the categories there is Search. There are two clickable boxes there. Your default search engine is in the box on the left. Click on the dropdown arrow and you can choose from among a bunch of different ones to use as your default.

I've got that setting changed already, i'm just trying to figure out why a Yahoo search page is the home page upon starting Chrome.

Edit: Click on link with caution, i'm not sure if it's legit.

http://us.yhs4.search.yahoo.com/web/partner?&hspart=w3i&hsimp=yhs-syctransfer&type=W3i_SP,203,0_0,StartPage,20120939,17093,0,11,0

Hmm, that's weird. I didn't try that link yet. Havea you tried uninstalling Chrome, then doing a reinstall?