There is no "Mozilla security", that's a fake scan to entice naive users to spend their money to install more Malware on their PC. Many times clicking on anything (even the Close X for the window) in that "fake scan" window can install Malware, the best thing to do is to kill the process that is running that "fake scan" via the Task Manager > Processes tab. Of course, you first have to try to figure which running process is causing that "fake scan" to run.

(Yeah, do as I say not as I do, I clicked to close it without thinking - I have been recommending this stuff for like 4 or 5 years now, AND I got caught by one of those a few weeks ago when I was checking a web site for another Firefox user. It took me 45 minutes to clean up after it and I had those programs sitting on a USB stick so all I had to do was to install the programs, update them, and run the scan. I used the 2nd one on the list, disregarding what I know the best order to be, and I had to run the first one to find and remove that garbage.)

Anti-virus programs don't scan for Malware, you need to use anti-Malware programs for that.

Install, update, and run these programs in this order. They are listed in order of efficacy.
(Not all programs detect the same Malware, so you may need to run them all to solve your problem.)
These programs are all free for personal use, but some have limited functionality in the "free mode" - but those are features you really don't need to find and remove the problem that you have.
Note: If your Malware infection is bad enough and you are mis-directed to URL's other than what is posted, you may have to use a different PC to download these programs and use a USB stick to transfer them to the afflicted PC.

Malwarebytes' Anti-Malware - http://www.malwarebytes.org/mbam.php
SuperAntispyware - http://www.superantispyware.com/
AdAware - http://www.lavasoftusa.com/software/adaware/
Spybot Search & Destroy - http://www.safer-networking.org/en/index.html
Windows Defender: Home Page - http://www.microsoft.com/windows/prod.../default.mspx
Also, if you have a search engine re-direct problem, it might be caused by a Rootkit - see this:
http://deletemalware.blogspot.com/2010/02/remove-google-redirect-virus.html

Thanks for your prompt reply. They're so tricky - - I saw Mozilla and just trusted it and did what I was told to do.

Anyway, I have an external hard drive. I've been told that if you have a virus on your computer, if you hook up your external to it, you could get the virus on the external also. Is that true with malware? Will it be safe to hook up my external to the computer now? (I haven't run the malware programs yet.)

Also, how do you know that you have found the malware problem? I don't really notice anything different with the computer - - except that sometimes you hear the computer running alot when I don't really think it should be. That has been going on for a long time, so maybe that is malware running something in the background?

Thanks for your help. I'm not very computer savvy - - so it's great to have somewhere to turn to when you run into problems. Now if I can just use these malware programs correctly!

Deb Windows XP