This is definitely not something that happens on a regular basis, and yet it happened recently. Aaron Swartz was the reason behind the hacking of two U.S. government websites a while back, and it was in response to the suicide of Aaron. From what I understand, here is what took place. This is from the source page located at PCMag:
"Swartz, who helped develop RSS, was an activist who ran afoul of the law after downloading portions of the JSTOR academic paper database. Swartz apparently intended to distribute the papers for free, an act of protest over JSTOR's business model, which led to him facing a maximum of 35 years in prison.
He committed suicide in his Brooklyn home earlier this month. Swartz's supporters blame investigators and prosecutors for his death, whom they claim overstepped their authority."
"A game of Nyan-cat flavoured Asteroids will begin if you enter the following 'Konami code': ↑ ↑ ↓ ↓ ← → ← → (up up, down down, left right, left right on the cursor keys) then press 'B', 'A' and 'Enter,'" writes Sophos. Once entered, a dialog box appears. It reads, "PEW PEW PEW PEW PEW! End Prosecutorial Overreach!"
A Nyan-cat image then appears in the middle of the page, controlled by the arrow keys. Pressing the space bar fires a weapon used to destroy the page's elements revealing a memorial tribute to Swartz. For those impatient, pressing "F" will release a bomb and blow up elements more quickly."