Rather endearing term coined (on slashdot?) at the start of the famous DeCSS lawsuits.

DeCSS was the first available program that cracks the encryption present on DVD movies, and allows the contents to be copied, re-compressed with DiVX and transferred over the net, or basically whatever you like. (more info here)

Bizarrely enough, with the cat so very much out of the bag, the Movie Studios decided that it would be a clever idea to start legal action against any website that either carried the DeCSS program (a mere 68k in size), the core source code it was derived from, or sites that even had a link to it.

This was a monumentally stupid idea, which predictably incensed almost everyone on the entire Internet, so unsurprisingly within hours there were tens of thousands of websites and other channels where you could happily download the offending decryption code. It's here on E2, in fact. People have even had it printed on T-Shirts.

Hence Wack A Mole - after the ancient (and very fun) arcade game where little moles pop up randomly out of a set of holes in the machine and you wack them on the head with a wooden mallet to score points. The more you wack, the faster they appear - until eventually you are snowed under by the sheer number and speed of them.