The Anonymous hacktivist collective claims it is responsible for putting a Washington public relations firm out of business.
But a former executive at the now-defunct company, known as The Bivings Group, denies the allegations.
Anonymous defaced the firm's website and hacked into a database, spilling the contents, including hundreds of corporate emails, the collective said in a Pastebin document, posted Monday.
Anonymous targeted The Bivings Group as part of "Operation End Monsanto," a campaign designed to go after the multinational maker of genetically engineered seeds and growth hormones.
The Anonymous operation appears to also include targeting related businesses, such as The Bivings Group, which performed public relations work for Monsanto dating back about a decade, according to LobbyWatch, a British organisation that monitors PR and lobbying practices.
In September, the company's former vice president Todd Zeigler launched Brick Company using assets acquired from the Bivings Group.
Zeigler denied Anonymous was responsible for the closure of the Bivings Group.
"The launch of the new firm is something that has been in the works for a few years. The attacks attributed to Anonymous had no impact on our decision to launch the new firm."
He did not describe what the attacks entailed.
The Bivings Group has come under fire in the past. In 2002, a writer for the Guardian described how the now-defunct business was responsible for leading a campaign in which fictitious doctors barraged listservs frequented by scientists to disparage a Nature science journal paper detailing how genetically modified corn contaminated native Mexican corn.
Ultimately, Nature retracted the paper, reportedly the first time in its then-133-year history.
The Bivings Group reportedly said the claims were unfounded.
A Monsanto spokesman did not respond to requests for comment on Thursday.
In June, Anonymous, upset over Monsanto's business practices, leaked the names, addresses and phone numbers of 2,500 employees and associates.