Well, you can search your computer for images and video's, and if you find illegal stuff on your computer then I guess that would answer your question as to whether or not you had some kind of malicous software or trojan running in the backround of your computer..these types of trojans are starting to become more of a problem, or so I've been seeing in the news anyways. It really is a scary thought, ecspecially with the penalties and the stigmas that come with these kind of issues. You can just get a new hard drive if you're really paranoid, but from what you described happening, I really don't feel thats needed. I'd imagine this has happened to alot of people..I mean think about ALL the people that search for pron every day. Think about ALL the people that use the internet without any security features. You're not the first person this has happened too, and you're deff. not the last either. I would get that ERASER program I mentioned earlier and let it run its course for some peace of mind, but other than that I really wouldnt worry about this too much. Really.