WHAT'S HAPPENING: Knight Capital is the trading firm that had a technical problem Wednesday that briefly threw off stock trading. Knight has been under pressure since then, working to convince clients that it has everything under control. It's reportedly considering whether it needs to sell itself.

WHY THE BIG FUSS? Knight's blunder is part of a bigger, thorny debate about the merits of stock trading being performed by superfast computers and complicated algorithms, which now account for far more trading volume than floor traders in colorful jackets. Previous episodes have rattled investors, such as the 2010 "flash crash," where a computer problem sent stocks down wildly.

THE LATEST DEVELOPMENTS: It's impossible to predict if Knight's mistake will be its undoing, or just an error that people quickly forget. The company did get some breaks on Friday. Its stock jumped after being pummeled for the past two days. One client, TD Ameritrade, announced that it had resumed routing trades normally through Knight. The Wall Street Journal reported that the company got a new line of credit.