I've had a few things happen to me with my computer that was kind of spooky.
I just want to say that I'm a systems engineer so I know a thing or two about my computer and the operating system - just wanted to get that out first.
First thing that happened was every once in a while there would be this song "bad to the bone" playing - just the chorus for a few seconds, playing from the sound card. It didn't matter what applications I had open and I never found the source of the sound. I think it went on for something like a few months until I finally reinstalled the OS. I had A/V software and did several full scans but never found any viruses or malware. Extremely weird but it didn't scare me as much as it intrigued me - that's why I didn't reinstall as soon as it happened the first time.
Second incident, I had downloaded a movie on my computer that I was planning to copy over to my phone to watch during a trip, I download the movie and inside is an .nfo file or something, I can't recall what kind of file it was that came with the movie but i think it was an .nfo, anyways, inside this file is the XML from an Android app (I use android), I'm guessing that it is how an .apk looks when opened in notepad, so I go through the file a little bit to see what I can find out about what I at this point think is an attempt to "smuggle" in an APK into my Android phone. I then close the file and start to do some research to see if this is normal in the "hacking community" and if its a viable way to compromise phones. I then go to open up the .nfo file again as I want to show a friend what it looks like and its just a normal .nfo file with the info about the movie, who made it and such stuff - just a totally normal text file.
At this point I really start to freak the fuck out since I am totally sober, not tired or anything - basically at my best mind-wise and I am 100% sure it was an Android app, likely an APK inside this file just a few minutes earlier. I turned on every indexing options I could find in Windows and tried to search through all the files on my disk for some keywords that I could remember from the app but I never found it again, and I had never downloaded any APKs to my computer before this. I have no idea what the hell was going on - one second the .nfo file is an android app and after just like 30 minutes or something its back to being a normal text file again. That freaked me out and I ended up reinstalling the computer OS and also reflashed the phone OS to stock (I think i had cyanogenmod before).