People are borrowing computer access codes from brokerages to make rapid-fire trades directly on exchanges, all under the cover of anonymity. Gee, what could possibly go wrong?

That's what regulators are trying to figure out. They're examining whether giving "naked" access to high-speed traders could potentially screw up the markets, according to The Wall Street Journal.

Firms have ramped up computers to trade billions of shares a day, and the tradebot strategy has paid off handsomely. So much so, in fact, that those high-speed trades now account for more than half of all stock-trading volume, the Journal reports. 

Here's how it works:  Regulated brokerages have computer access codes that allow them to trade directly on exchange computers, according to the Journal. These brokerages are loaning out those codes -- at high fees, of course -- to hedge funds and other firms.

Stock exchanges and regulators have no idea who is renting these codes. All they see are high-speed trades coming in under the regulated brokerage's name.

With the trading now being done by computers, it's pretty safe to assume that something will go wrong. And one could imagine a major trading glitch -- like a wave of high-speed orders triggering other waves -- causing a broad decline in the overall market. 

Now, brokerages said they make continuous posttrade checks, and can stop a computer gone wrong. But the Securities and Exchange Commission is investigating whether the stability of the markets are at too much risk here.