May 7 (Bloomberg) — U.S. stocks tumbled the most in a year as waves of computerized trading exacerbated a selloff triggered by Europe’s debt crisis, sparking a slide in Asian shares. The rout briefly erased more than $1 trillion in U.S. market value as the Dow Jones Industrial Average fell almost 1,000 points, a 9.2 percent plunge that was its biggest intraday percentage loss since 1987 and largest point drop ever, before paring declines.

The U.S. Securities and Exchange Commission and the Commodity Futures Trading Commission are reviewing “unusual trading” that contributed to a plunge in U.S. equity markets.

Nasdaq OMX Group Inc. said it will cancel stock trades on all exchanges that were more than 60 percent above or below prices at 2:40 p.m. New York time, just as U.S. equities plummeted. Nasdaq said it will provide a list of stocks affected and the prices at which the trades will be canceled. The decision cannot be appealed, Nasdaq said.