I’ve got a stubborn trojan that Ad-aware and Spybot and AVG can’t seem to get rid of. I tried downloading Malwarebytes on recommendations from the Dope, but if I try to install it, it doesn’t. Or, a couple of times, I’ve managed to install it, but then it won’t run. This has happened with a few different anti-malware programs. I’m downloading them from download.com, and I’ve got a Compaq Presario running XP.
Help!
Probably the malware is blocking the ability of the anti-malware program to properly install and run. 
That’s what I was thinking. Crap.
Find and download a program called SDfix. it will only run in safe mode(restart computer and tap f8 until start menu pops and select “safe mode”
You will need to install it in regular mode however.
Malwarebytes can also be installed in safe mode, and the task that is blocking it might not be running in safe mode.
When we get things like this in my shop we pull the hard drive and scan it with another machine. Works great if that is an option for you.
Like you, I had trouble accessing anti-malware software and running it. But then I found a helpful person named Jintan at Malwarecrypt.com, whose heroic efforts over the course of several weeks helped me rid my computer of malware. So you’re in for a slog, perhaps, though it should come right in the end.
I had a similar problem a while ago. I found that renaming the Malware installer program to something else (anything else) allowed it run and install properly.
Give Super Antispyware a try. The malware doesn’t know to block it yet.
Threatfire is good as a preventive measure. I really like the way it works.
I had threatfire installed and I still got the Conficker virus, so I don’t know if that’s going to be all that much of a help. Needless to say, I was quite ticked. I removed threatfire and went with AVG. AVG bogged my machine down so bad I could hardly do anything. I’ve now switched to Avira and hope that will be the solution to my security needs (along with my firewall program)
You may want to check for Conficker on your machine as well, just to be safe. The inability to update my security programs is what alerted me to its presence. Go here for a quick “eye test” for it:
http://www.confickerworkinggroup.org/infection_test/cfeyechart.html
Threatfire or not, the way malware is promulgating, you can get it no matter what antivirus you have – even if you updated it today.
As for Conficker, you probably had it on your machine before you installed Threatfire (and after the trigger date). Conficker probably wouldn’t be noticed by Threatfire unless you did a scan. Threatfire looks for malware activity and I could see it missing Conficker while it was dormant – but it should catch it once triggered.