Anonymous has posted names, addresses, phone numbers and email addresses of Monsanto employees, and is promising action against Exxon Mobil, ConocoPhillips, Canadian Oil Sands, Imperial Oil, the Royal Bank of Scotland and others.

In the case of Monsanto, the hacker group has posted information about 2,500 employees and affiliates of Monsanto and claim to have taken down corporate websites and mail servers, according to Sophos Naked Security.

Anonymous didn't indicate how it broke into the network but mentioned that port 6666, used for IRC chat, was opened. The port can be used for introducing Trojans and worms that can infect IRC servers and clients.

The group says it is setting up a Wiki where the data it stole from Monsanto can be posted, Sophos says.

Monsanto could not be reached immediately for comment.

Meanwhile, Anonymous has posted its intent to protest against Exxon Mobil, ConocoPhillips, Canadian Oil Sands, Imperial Oil and the Royal Bank of Scotland for their role in extracting petroleum products from tar sands in Alberta, Canada.

In what it calls Operation Green Rights, the group throws its support behind protesters in Montana who view the extraction as an environmental threat. "We will, over the course of the next few days, use the powers we posses to spread news about this scenario and the corporations involved. We are actively seeking leaks to expose the corruption that we all KNOW is beneath this," Anonymous said.

News of the Monsanto attack came about the time when one Anonymous Twitter account said that July 12 would be the biggest day in Anonymous history, but the Monsanto incident doesn't seem to fit the bill. In the past, for example, the group has taken down MasterCard's website and exposed volatile emails stolen from HBGary Federal.