I'm not certain what it is, exactly. I think it might have been a worm that my anti-virus ignored because it looked normal, like a regular program. It apparently tries to connect itself to the internet when one logs on normally, but Internet Explorer cancels out the intruder, which then prompts the "uwaga!" message. Or something along those lines. Anyway, I ran Task Manager to check what processes were running and I saw one I hadn't seen before: mobcx.exe. I ran a search for it and found it in a system folder in Windows.There was another file with the mobcx prefix, a .pf file, in another folder entirely. I deleted mobcx.exe and the .pf file, and that seemed to work.