(Bloomberg News) The U.S. Securities and Exchange Commission halted trading in 379 shell companies over concern that fraudsters could hijack stocks to steal investor money.

The trading suspensions, the most by the SEC in a single day, stem from the work of an agency task force that identified clearly dormant microcap stocks in 32 states and at least six countries, the SEC said today in a statement.

Microcap shares have long been used for frauds such as pump-and-dump schemes, in which a perpetrator buys stock in a thinly traded company and touts its value through false and misleading statements. Illicit profits are reaped when those behind the fraud dump their shares into the market after pumping the prices higher.

"Empty shell companies are to stock manipulators and pump- and-dump schemers what guns are to bank robbers -- the tools by which they ply their illegal trade," SEC Enforcement Director Robert Khuzami said in the agency's statement. "This massive trading suspension unmasks these empty shell companies and deprives unscrupulous scam artists of the opportunity to profit at the expense of unsuspecting retail investors."

Regulators sharpened their focus on shell companies about two years ago amid complaints that issuers, many from China, were using them to enter U.S. markets through so-called reverse mergers. In a reverse merger, closely held firms buy shells that let them sell shares on exchanges without the scrutiny that would surround a public offering.

Several reverse-merger companies have seen their share prices plummet amid allegations that their financial statements were inaccurate.