Answer by taking a quote from the following article:

Cuban was born in Pittsburgh, Pennsylvania. His father, Norton Cuban, was an automobile upholsterer, while Cuban has described his mother, Shirley, as someone with "a different job or different career goal every other week." He grew up in the suburb of Mount Lebanon, in a Jewish working-class family. His paternal grandfather changed the family name from "Chabenisky" to "Cuban" after his family emigrated from Russia through Ellis Island.

On November 17, 2008, it was reported that the U.S. Securities and Exchange Commission (SEC) filed a civil suit against Cuban relating to alleged insider trading in the shares of Mamma.com, now known as Copernic. A stock dilution occurred shortly after a trade in June 2004, giving hints of inside knowledge at the time of the trade, and Cuban allegedly was saved from a loss of $750,000. The SEC claimed that Cuban ordered the sale of his holdings in Mamma.com after he had been confidentially approached by the company to participate in a transaction likely to dilute shares of current shareholders. Cuban disputed the charges, saying he had not agreed to keep the information secret. On his blog, Cuban contended the facts were false and that the investigation was "a product of gross abuse of prosecutorial discretion". DealBook, a section of The New York Times, reported through an anonymous source that Cuban believed the investigation was motivated by an SEC employee having taken offense to his interest in possibly distributing the film Loose Change.  In July 2009, the U.S. District Court dismissed the charges against Cuban, and the SEC appealed. In September 2010, an appeals court said that the district court had erred and that further proceedings would be necessary to address the merits of the suit.  A federal jury in Texas found in favor of Cuban on October 16, 2013. The nine-member jury issued the verdict after deliberating 3 hours and 35 minutes.  In March 2014, Cuban was on air at CNBC criticizing high-frequency trading (HFT). Those against HFT, such as Cuban, believe the technology is equivalent to automated insider trading.

What was the allegation about?
it was reported that the U.S. Securities and Exchange Commission (SEC) filed a civil suit against Cuban relating to alleged insider trading in the shares of Mamma.com,