IBM's share price just dropped by a whopping 25%. That's thanks to IBM's CEO, Arvind Krishna, saying the company didn't adapt quickly enough to the industry moving towards spending less on software and more on data centre infrastructure (via CNN).
As noted by CNN, this puts the company in the vicinity of its worst day ever, which was Black Monday in 1987. Although it should also be noted that this steep drop occurred during pre-market trading, which tends to be more volatile than in-hours trading. We'll have to see where the chips actually fall by the end of the day.