Used to be called the Slashdot effect; nowadays you see it more in reference to Reddit. There should be a name for it that doesn't need to change every time a new web link aggregator becomes flavour of the month.

Incidentally, whatever it's called, "hacked" is not the right terminology. Whether you're of the belief that "hacker" means "programmer" or "evil nasty person", this doesn't qualify for the term.