As if investors didn't have plenty to worry about already, technology-driven trading snafus are starting to add up for the nation's stock markets. Nasdaq's recent three-hour shutdown, due to a software flaw, halted trading in the exchange's 3,300 listed securities, including Apple, Google and Facebook. The so-called flash freeze followed last spring's #HashCrash, when the Dow Jones industrial average plunged 144 points in two minutes after hackers posted a fake tweet about an explosion in the White House. And that followed the nearly $1 trillion plunge in 2010, known as the flash crash, that was tied to one investor's flawed trading algorithm.

Cyber crime, too, is a major worry. In a recent survey, some 53 percent of the world's securities exchanges said they had suffered a cyber attack in the past year. Attacks so far have been aimed at disruption rather than financial gain. Still, 89 percent of exchanges surveyed agreed that cyber crime poses a systemwide risk to world securities markets.

Are tech-driven disruptions, whether malicious or accidental, an inevitable part of modern life? Or are they an indication that markets -- and regulators -- have failed to keep pace with lightning-fast technology?

The more complex the system, the more parts that can break, says Georgetown University finance professor James Angel. But, he adds, "everyone is breathing down the exchanges' necks" to reduce the risk of such malfunctions. Earlier this year, the Securities and Exchange Commission proposed rules that would compel exchanges, trading systems, clearing agencies and others to develop, test and maintain their systems to make sure that certain technological standards are met. A summer cyber-security exercise called Quantum Dawn 2 tested the industry's capability to respond to a cyber attack.

Still, critics contend that the markets have become too fragmented and too fast-paced. There are now 13 separate exchanges and some 50 so-called dark pools (trading venues for institutional orders, which are unavailable to the public), and each has different technology, operating speeds, order types and rules, says Sal Arnuk, of brokerage Themis Trading. "There's no way you can eliminate the chance of failure in such a complex mousetrap."

But although the recent debacles can undermine confidence, they shouldn't loom large for most individual investors, says Larry Tabb, of the Tabb Group, a financial-markets research firm. The markets operate efficiently most of the time, and investors with a long-term perspective shouldn't be tremendously concerned about short-lived derailments. Still, to play it safe, make trades using limit orders, which allow you to buy or sell securities at a specific price or better.

(Anne Kates Smith is a senior editor at Kiplinger's Personal Finance magazine. Send your questions and comments to moneypower@kiplinger.com. And for more on this and similar money topics, visit http://www.Kiplinger.com.)

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