Something attacking Firefox, and my anti-malware! Help!

Hi folks. First off, I wanted to say kudos for running what appears to be a very effective and helpful site.

Unfortunately, I didn't come by MajorGeeks today just to tell you I think you're doing a good job. Last night while surfing some pages, I noticed a drastic slowdown in my computer's performance. I tracked down the unfamiliar programs in my processes list, found where they were installed to, and started trying to get rid of them. One went without much of a fight, but the others which looked suspicious anyway, were giving me some trouble upon my attempts to delete them.

Being worried now, I went to run Spybot: S&D, as it's always done a lot of good for me. This is when I got really worried, as shortly after starting a scan, the program simply disappeared very suddenly. I tried restarting the program, only to be met with an error message telling me that I might not have the proper permissions to run the program. I then tried Ad-Aware, to see if that might find the problem by some chance, only to be met with a similar problem. The trick was, my license on my anti-virus had expired, and I hadn't yet gotten a replacement, which I'm sure is the cause of my problems to begin with.

The other problem here is that when I went to try and re-install spybot, I couldn't get to the proper download page. When using Firefox, my default browser, certain pages just seem to crash the browser. The sites that do this seem to have no discernibly common theme. I can check my mail, read a few webcomics, but anti-malware sites, other webcomics that I trust, Wikipedia pages, they just close everything down. The sites that do it seem consistent, but the types of pages don't.

At this point, I was a bit freaked out, and a friend told me they use Avira for their anti-virus protection, and luckily I was able to get to the page, and install that. It's been working well throughout this process, and seems to be the only protection program I've been able to keep running. It found a number of potential problems, and deleted those files I was having trouble with before. Most of the problems I was having are cleared out, which I'm glad for, but a few are still remaining. Firefox is still not able to go to those sites, and crashes when I try, and I can't seem to effectively re-install spybot.

I got the download from IE, but when I try to re-install, I get an error message about the file "SpybotSD.exe" itself being read-only, and the program doesn't run after the installation. I tried getting a hold of MalwareBytes, since I've heard good things there, but had the same problem where it would install fine, and then it would start a scan the very first time, then crash, and not start up again. That was about when I found this site, and started going through the READ & RUN ME FIRST list. CCleaner has been able to do its thing just fine, and I got rid of an old copy of Norton that wasn't doing anything anyway, I'm just starting to run out of ideas, since I can't run most of my relevant programs, and my internet capabilities are as damaged as they are.

Any help you could offer would be much appreciated.

 

UPDATE:

Not to bump myself pointlessly, but I wanted to add an update: it would seem that whatever it is has gotten its claws around Avira, too. So, I no longer have any ability to scan.

Please, if anyone has any ideas, pass them along. Thanks so much in advance.

 

Hi Tim, thanks for getting back to me.

So I was going about the steps you gave me here, and I've run into a problem. Everything was going alright here until step 5. Whenever I go to run FixAVP.exe, a command prompt window opens for just a minute, then closes again without ever trying to run Avenger, or asking me to reboot my computer. Could this just be some sort of mistake I've made? I don't see how I could have messed up there.