The US Securities and Exchange Commission has taken the drastic step of suspending trading in shares of 35 companies whose stocks are frequently touted in pump-and-dump spam scams.

SEC officials said that the firms involved - none of which are household names - have been the subject of repeated spam efforts meant to drive up the value of their shares.

The trading bans will last for 10 days, after which the shares will be unlocked - unless the SEC's ongoing investigation proves any of the firms were involved in the email schemes.

While the ban might seem unfair to the businesses involved, especially if they were merely selected by scammers looking for penny stocks to inflate, SEC officials said that in each business's case, there were sufficient questions raised regarding the "adequacy and accuracy" of information being advertised about the companies.

Criminals are increasingly using spam to drive up interest in cheap stocks. Before sending out mass messages about a specific firm, they buy stock in the companies in the expectation that they can convince other people to purchase shares. When prices of the shares rise, the schemers sell off their own holdings, thus the pump-and-dump moniker.

The spam messages, which often feature subject lines such as "Fast Money," have become one of the types of unwanted email most frequently delivered to in-boxes over the last year, alongside advertisements for prescription medications.

Whenever misleading information is being widely distributed about a firm whose securities are traded, the SEC takes such actions, an agency representative said.

"All we can say is that we suspend trading any time we think misinformation about specific securities is being reported," said Helene Glotzer, an SEC spokeswoman. "We're not making a statement that these companies themselves were behind the misstatements, but if the information is out there we feel it is important to let the investing public know; we'll continue our investigation, and if it is appropriate to take action against any of the companies, that is what we will do."

The suspensions are part of an SEC initiative known as Operation Spamalot, which was launched specifically to shield investors from spam "hyping" small stocks.

The frozen stocks are are among those used most frequently in securities-related spam campaigns. The messages typically advertise some new product or impending deal that will increase the value of the companies and encourage investors to buy their low-priced securities.

For instance, among the companies whose shares were suspended is Apparel Manufacturing Associates, which markets itself as a management and development company focused on the fashion industry.

The SEC said that on Friday, 15 December, shares in Apparel Manufacturing closed at 6 cents, on a trading volume of 3,500 shares. After a weekend-long spam campaign using emails about the company advertising "huge news" that encouraged investors to "get in before the wire," trading volume in the stock rose to 484,568 shares on 18 December, with the price of the stock rising to more than 19 cents a share.

The agency said that two days later the price had climbed to 45 cents per share, but one week after, Apparel Manufacturing's share price had fallen to 10 cents on trading volume of 65,350 shares.

Calls to the company seeking comment on the stock suspension were not immediately returned.

If the SEC investigation finds no link between the companies involved and the spam campaigns, their shares will be released for trading on 21 March.

SEC officials noted that the suspensions were all handed out to companies that are not subject to the SEC reporting requirements and whose shares are not listed on any exchange or on the OTC Bulletin Board. This means that brokers posting quotations for the purchase and sale of the securities are not required to conduct due diligence regarding the issuers, according to the agency.

The 35 companies whose trading was suspended by the SEC are: Advanced Powerline Technologies, America Asia Petroleum, Amerossi International Group, Apparel Manufacturing Associates, Asgard Holdings, Biogenerics, China Gold, CTR Investments & Consulting, DC Brands International, Equal Trading, Equitable Mining, Espion International, Goldmark Industries, GroFeed, Healtheuniverse, Interlink Global, Investigative Services Agencies, iPackets International, Koko Petroleum, Leatt Corporation, LOM Logistics, Modern Energy, National Healthcare Logistics, Presidents Financial, Red Truck Entertainment, Relay Capital, Rodedawg International Industries, Rouchon Industries, Software Effective Solutions, Solucorp Industries, Sports-stuff.com, UBA Technology, Wataire Industries, WayPoint Biomedical Holdings, and Wineco Productions.