The SEC suspended trading in 61 empty shell companies Monday, the second largest group of companies to be affected by a suspension order in one day in the agency’s history, the SEC announced.

The suspension order is part of “Operation Shell Expel,” which is a crackdown on the manipulation of microcap shell companies that are ripe for fraud, as they lay dormant in the over-the-counter market, the SEC says.

The companies, which are located in 17 states and one foreign country, are delinquent in their public filings and seemingly no longer in business based on an analysis by the SEC's Microcap Fraud Working Group.

Once the companies become dormant, they have great potential to be hijacked by fraudsters who falsely hype the stock to portray it as a thriving company and coerce investors into “pump-and-dump” schemes, the SEC says.

By suspending trading in these companies, they are obligated to provide updated financial information to prove they are still operational, essentially rendering them useless to scam artists because they are no longer operating in the shadows, the SEC adds.

Pump-and-dump schemes are among the most common types of fraud involving empty shell companies. Perpetrators tout a thinly-traded microcap stock with false statements about the company to the marketplace. They then purchase the stock at a low price before pumping the stock price higher by creating the appearance of market activity and drawing investor interest. They dump the stock for significant profit by selling it into the market at the higher price once investors have bought in, the SEC explains.

The largest suspension of trading in dormant companies in one day took place in May 2012 when the SEC suspended trading in 379 companies.

At the time that suspension was announced, Robert Khuzami, then director of the SEC’s Division of Enforcement, said, “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. 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.”