I downloaded and ran an exe, expecting to get a user manual. Instead, FileFinder icon appeared on my desktop. Also when I run Firefox, for which I normally have no home page, I see a variety of home pages, including tech-connect.biz, ww.reimageiplus.com and winhugebonus.com. On one Firefox startup, I was asked to call a 1 844 number to have someone fix the problem: sounds like Ransomeware to me.

I am able to run Firefox OK. The chances of my clicking on the malicious home page are few.

Is my PC compromised, and if so how?

I am running Win 7 SP1 with all important updates and SS&D Professional. I don't use Outlook, and I store passwords on a USB stick that is plugged in only when needed (which is seldom).

If it is compromised, how should I proceed?