When we created battle.net at Blizzard for Diablo, there was a bug where the game would launch in full-screen mode and hang, and the only way to escape back to the Win95 desktop was to click the ad displayed by battle.net.

We weren’t aware of this.

The ad company we used notified us of this issue and gave us three days to fix it. Afterwards our click-through rate went from something like 3% to .25%.