Malicious or not? Message popped up: Mozilla security found (something like too much, forget exact word) activity on your computer so it will do a fast scan of system file. With OK button.

Question

I was looking at youtube.com, which always tells me my browser is not supported and recommends I download Firefox, but that is what I was using, so I went to Firefox to check for updates. (I think I also had freecycle.org open.) Then this message popped up in a new page: Mozilla security found (something like "too much", forget exact word) activity on your computer so it will do a fast scan of system file. There was an OK button. The page address was: http://update17.stegner.ce.ms/index.php?Q7Lhl9ShbRxGJXpkM1VLSi4ZE8H4pTedoVPySgeppM3VpC+thEspcFG7qxHgn1pdsC2h5ygPGWI3t5hXqMzL9EQaZZ3J1e3CKXgCb0Qp. I did not click OK but copied the link and closed the window which closed the internet. I have never seen this before and would like to know if it is really Mozilla or possibly something malicious. Thank you.

Answer 1

Good catch. That almost certainly is an invitation to download malware.
There are a lot of infected web sites pushing "fake antivirus" software. If you have any doubts about whether your system might have become infected, you can supplement your regular security software with these two highly regarded scanners:
Malwarebytes Anti-malware : http://www.malwarebytes.org/mbam.php
SUPERAntiSpyware : http://www.superantispyware.com/