© NY TimesLulz Security claimed responsibility for knocking the Central Intelligence Agency’s Web site offline last week.

The Internet may be about to get a little more chaotic than usual. Over the weekend, a group of hackers declared that they are initiating cyber warfare with governments and security companies around the world.

The group, Lulz Security, has claimed responsibility for a number of recent data breaches and have already attacked a number of United States government and corporate Web sites. Lulz Security also said it was working closely with another group called Anonymous, a loosely affiliated team of activist computer hackers. Although Anonymous did not put out its own statement about the attacks, the two groups have been communicating regularly on Twitter.

In a letter posted on a public Web site, Lulz Security announced its plan to attack more government sites and encouraged other groups and individuals "to open fire on any government or agency that crosses their path." The undertaking is called "Operation Anti-Security."

"Top priority is to steal and leak any classified government information, including email spools and documentation," Lulz Security wrote in the letter. "Prime targets are banks and other high-ranking establishments."

The Federal Bureau of Investigation declined to comment on the letter.

Last week Lulz Security breached the Web server of the United States Senate and briefly brought down the Central Intelligence Agency Web site through a denial-of-service attack. The group has also been responsible for attacks on Sony, Bethesda Softworks, a gaming company, and a string of other sites.