Actually, for a patent (and, as someone pointed out, it's a trade mark the orignal article is about) if there is documented proof of a previous invention (I doubt that would be a problem with IT) that is the easiest was to invalidate a patent.

For trade marks, fame does matter, but then again: documented previous existence of a smaller brand would be enough to stay. Having one large corporation buy a small existing brand, and marketing it beyond its original scope could put them in trouble, though.