Not long ago, Google was sued by Northeastern University who claimed that they had infringed on search technology they owned. Given that Google's entire empire is based upon search technologies, you can imagine they were more than a little irked. So irked, in fact, that after outright denying they have done anything wrong, they have filed a counterclaim against the University.
Google's argument is that the patent they are being sued over shouldn't have been issued in the first place and is invalid. Their counterclaim doesn't demand huge sums of money, only that the patent is invalid and can't be enforced. In either instance, the case is heading to trial and now Google will be battling them in the courts.