UPDATE: Zecco reports in its company blog that it was not an April Fools' Joke, but a vendor error that happened to occur on April 1:

"On April 1, 2009, one of our vendors provided Zecco Trading with an incorrect data feed which caused some customers to see erroneously high buying power. This error was quickly corrected, but about 1% of our customers were impacted. All positions in excess of our customers' true buying power have since been closed. Except in a very small number of egregious and fraudulent cases, customers will not be responsible for losses (or gains) incurred for trades in excess of their buying power.

Additionally, we want to make it clear that contrary to some reports, this was not in any way intentional and was not an April Fool's joke. We take the integrity of our customers' accounts very seriously and we have taken measures to ensure this does not happen again. We sincerely apologize to our customers if this caused any confusion. "

Last week Zecco, an online brokerage based in Pasadena, California, apparently tried to pull off maybe the dumbest April Fools' Day prank of all time. According to The Consumerist, a consumer advocacy site, Zecco made it so that when its users logged in, their account balances appeared to mysteriously skyrocket by millions of dollars. Hi-larious.

Only Zecco customers started buying stocks with their newfound riches. Consumerist posted some Zecco customer complaints from an online forum, including one from a user who claims to have used the funny money to buy stock, which Zecco immediately sold at a loss. Zecco then deducted the loss from the user's account, as well as a $20 commission fee.

Here's a tip: If you're going to punk people into thinking they are rich, make sure they can't actually spend the money!