This popup very infrequently appears.
I've just worked out that it appears to be your icon in the corner. Oh, if only I had 20/20 vision.
Do you think you could see your way to putting a clue in the popup's text as to its origin or to indicate what it's about, and maybe what action should be taken? Otherwise, it looks suspiciously like one of those fake virus alerts that try to get users to install nasty stuff "Our free virus scanner found (5) viruses. Click 'OK' to remove them."?