Cloned items were a nuisance in Diablo II but the addition of a real-money auction house to Diablo III makes trading serious business--actual business, in fact. Anything which disrupts the market will inspire far more fury when people can earn actual cash money, so Blizzard should be extra vigilant. No surprise, then, that the recently-publicised invulnerable wizard bug has been hotfixed out, though it may have been exploited by players for quite some time.
"We are currently rolling out a hotfix for a recent bug regarding invulnerable Wizards," Blizzard said in the wee small hours of the morning. The developer urges players to formally report any exploitable bugs or hacks they may find.
However, while the bug has only recently received widespread attention, it may have been around for far longer. A YouTube video seeming to demonstrate the bug was uploaded on June 22, so people could have been exploiting this for at least a month--they simply didn't spread the knowledge around everywhere.
Inspired by how soon this was fixed after it went public, one player has already shared an old Barbarian exploit which gives huge amounts of life leech, hoping Blizzard will act quickly.