Amid the general goofiness of April Fool’s Day, one prank has turned into a business opportunity for AdBlock, the most popular add-on for Chrome and Safari.

AdBlock developer Michael Gundlach celebrated the occasion by having the add-on replace every online ad with a picture of a cat, instead of its usual practice of making the ads invisible to AdBlock’s more than 4 million users.

True to the spirit of the Internet, Gundlach explained the joke in a blog post purportedly – purr-portedly? – written by the cat programmer. The feline wrote, in perfect lolspeak, that AdBlock was too boring before being imbued with kitteh.

Gundlach had included a option to disable CatBlock, expecting that not everyone would appreciate the humor. What he hadn’t expected, however, was the interwebs’ inexplicable affection for all things feline. So many people contacted him with a plea to make it permanent that he is turning CatBlock into a source of revenue.

Anyone who signs up to donate $10 a month will receive a stand-alone version of CatBlock, along with a thank-you note and a haiku. A monthly commitment of $20 or more gets more perks, including a drawing, the right to decide the topic of the haiku and more.

AdBlock itself will revert to its normal function in a day or so. And incidentally, Gundlach doesn’t have a cat.

Related links:

CatBlock – blog post

CatBlock – donation page