A long time ago I read some cyberpunk novel, and one of the characters had an ocular implant that got infected with malware that flashed spam ads for Indian brothels in his vision 24/7, even with his eyes closed, until he went completely postal.
Edit: oh heck. It might have been The Diamond Age.
Edit 2: search yielded
"Bud knew a guy like that who'd somehow gotten infected with a meme that ran advertisements for roach motels, in Hindi, superimposed on the bottom right-hand corner of his visual field, twenty-four hours a day, until the guy whacked himself." --Neal Stephenson, The Diamond Age