Investors would hear about the companies through newsletters emailed from websites that tout penny stocks, with names like PennyPic.com, OxofWallStreet.com and MonsterStox.com, their missives full of hyperbolic language and exclamation points.

What the investors did not know, prosecutors say, is that the men writing the newsletters owned stock in the companies they were promoting, and also had colluded with officials in those companies to drive up prices with misleading news releases.

When prices rose, the promoters and company officials would sell off millions of shares they controlled, leaving investors with worthless stock. It was an Internet-driven variation on the pump-and-dump stock manipulation schemes that unscrupulous stockbrokers have practiced for decades, prosecutors said.

On Thursday, eight people were indicted on charges they defrauded thousands of investors of more than $290 million from April 2009 to May 2012, using emailed newsletters to hype nearly worthless companies.