A Japanese unit of Switzerland's UBS said its computer systems mistakenly placed a $31 billion order for convertible bonds (CB) of videogame maker Capcom on Wednesday, but it was able to cancel the trade at no cost.

After largely fading from public consciousness following the dot-com bubble, day traders are back with a vengeance. But they're much different today from the 1990s image of someone in sweatpants trading at home.