So I consider myself a pretty conscious computer user. I run Windows 7 SP1 Pro 64bit and I update it. For surfing on the web I use Firefox 20.0.1 - I keep it updated. I also have NoScript and AdBlock - both up-to-date and running all the time. If I trust a site, I allow scripts from it (sites like stackoverflow etc.). For virus protection I use MSE - I know it's apparently not the best free software out there, but I though it'd be sufficient. Ill also point out that I dont forward any ports to this PC.
On the 6.05 at around 10:00 I started to browse the internet. I visited sites like stackoverflow.com, teamliquid.net and others - generally sites which I trust. I also visited sites which contained information about MPI protocol, but as far as I recall, I didn't allow scripts to run on these sites.
At about 11:00 I went to bathroom. When I returned, say at 11:30, I noticed that software was installed on my PC ('freshly installed', highlighted in menu start). I didn't notice this software before leaving to bathroom, it might have been there already, but I think it was NOT there yet.
So this software is called QType (quicktype apparently). It's somehow connected with other software - DealPly. They actually both got installed on my PC at that time, however only QType appeared as 'freshly installed' in my start menu. This software could also be somehow connected to 337 Technology Limited company. When I booted my browsers, they were both hijacked. Start pages looked like google, but it was in fact www.qvo6.com/... So in fact my browsers got hijacked.
So after seeing it, I went to view Windows' Event Viewer-> Windows Logs -> System to do some research. I noticed this message: Information; 2013-05-06 11:15:58; A service was installed in the system. Service name: Qtype Service ... Just after this one, this server entered the running state. There is no information about the other software - DealPly. Next thing I did was check what happened just before this suspicious service got installed while I was away. So in the event viewer system logs I can see, that something was happening with my browser: 'The computer brwoser service entered the running state.' and after a couple of seconds (six seconds in each log im looking at atm) 'The computer browser service entered the stopped state'. This rebooting of the service happened quite a few times.
So I wanted to ask those of You, who have some understanding in this matter. How is it possible that this software got installed without my knowledge. Was it some site I visited? Is it possible if I have disabled running scripts on sites? I may have accidentaly enabled scripts on some malicious site, but I don't think so. Is it possible that I didn't enable those scripts and it still got through somehow? Or is it something entirely different? Could it be some PDF I opened weeks earlier? (I sometimes read PDFs about stuff, like just recently about CUDA - but I imagine they come from trusted sites, of course this is naive reasoning). Or is it something else? Does the fact that this software got installed without my knowledge imply that someone has taken control over my PC?
I run a full scan of MSE - detected no viruses. Right now ill be running some anti malware software to get rid of unwanted things. Im considering re-formatting the PC - this would be the safest way, but I really don't like the idea of having to install all the IDEs and software again.
This infection really came as a surprise to me. Please feel free to answer if you think you can provide some insight on this matter and perhaps explain what took place on my machine, I will greatly appreciate your time.
I will also appreciate any tips to prevent such situation from happening in the future.