Like fubarubfusco says below, this is probably a malware issue. I saw something similar when a disk recovery program I didn't vet thoroughly enough infected me with a searchbar package that I'll leave nameless; MalwareBytes took care of most of it for me, though I had to do a little cleanup work myself.

It should probably be mentioned that most widespread antivirus packages won't catch this sort of thing; you need something that casts a broader net.