What was the worst bug you've ever solved ?
gdp: I inherited a giant hideous stock-management system.  It did a certain amount of automated ordering without manual intervention.Long story short: a nasty race condition meant that it was over-ordering duplicate products from the suppliers to the tune of tens of thousands of dollars per day.On the general theme, my most frightening software experience was when I met a guy who was the star programmer for a company doing controllers for elevators.  I got talking to him, and he showed me some code.  It took me about 15 seconds to identify an edge case that would engage the motor while the elevator was at the top floor (thereby attempting to pull the elevator into the roof?).  It took me a further hour to explain what the edge case was.  The bug wasn't that scary, as I'm sure there are hardware failsafes, but the general dimness of the guy writing software to control lifts was scary.I started taking the stairs after that.