Infinite Skills Hack
From Diablo Wiki
A classic example of a "hack" that wasn't actually a hack, just a way to take advantage of a bug in the game program. This "hack" worked by repeatedly equipping and removing any item with +1 to character skills. Thanks to the bug, the skill bonuses would remain, and stack up. Bored cheaters would click the same item on and off dozens or even hundreds of times, turning their character into a +1000 skill demigod, for the duration of that game.
This is godly for the Sorceress since virtually any skill she uses will kill everything with one hit. Barbarians with 25,000 hps from super high level Battle Orders are also being sighted.
Charged Bolt doing infinite damage is just silly. You get a Sorc with this using Thunderstorm in a dueling game, and it's instant death for anyone, making the game totally pointless. Reports are that getting skills to 1000 or more is the goal, since the damage is virtually infinite, and the mana costs seem to get screwed up and sometimes become negative.
This exploit came and went several times in early D2C patches, as it was fixed and then recurred repeatedly.