they can always call your college and ask if you were a registered student at any point in time. its not online, not in any sort of database at least.
usually they might ask you for your college transcript if its a first job or if youre a fairly recent grad. transcripts have to be notarized and are usually sent from the college to be considered "official".
but if youve been out of college for like 5-10 years i dont think they even ask for a transcript anymore. all thats for is a reference to get a sense of your background. if you've had a job since then, they would rather use that to gauge your compatibility. its really too much trouble to go and verify every degree a person might have on their resume, particularly because a lot of people might have gotten their degrees overseas.