U.S. Army Private Bradley Manning has been held in solitary confinement in a military prison in Virginia since the end of July 2010. (Associated Press)

A U.S. military base is the latest target of the online activist group known as Anonymous, which has taken up the cause of Bradley Manning, the U.S. army private accused of leaking classified information to WikiLeaks.

The group's objective is to "harass" the staff and disable the computer systems at the Quantico, Va., marine base where Manning is being held, Anonymous spokesperson Barrett Brown said in an interview with MSNBC.

The group plans to reveal personal information about base officials and disable the base's communication networks in protest against how Manning is being treated at the base, Brown said.

"It's sort of an unconventional, asymmetrical act of warfare that we've involved in," Brown said. "And we didn't necessarily start it. I mean, this fire has been burning."

Manning, who worked as an army intelligence analyst and had top-secret security clearance, was arrested in May 2010. He was later charged under military law in connection with downloading classified video and documents from military servers and passing them on to a third party. The material related to U.S. military operations in Iraq and also included thousands of diplomatic cables from U.S. embassies around the world .

He has since been moved to the military prison in Virginia, where he has been held in solitary confinement for months.

Anonymous is a loosely organized group that operates online whose members change depending on the cause the group is organizing around at any given time. It's not the first time the group has turned their attention to the issue of the WikiLeaks disclosures.

It targeted the websites of Paypal, MasterCard and Visa, which had limited or stopped processing donations to WikiLeaks and Manning's defence fund following the release of the U.S. diplomatic cables in November 2010. The sites were disabled mostly using what is known as a distributed denial of service, or DDoS, attack.

DDoS attacks function by programming large numbers of computers to simultaneously attempt to access one site, which is overwhelmed with empty traffic to the point that it becomes inaccessible. Depending on the scale of the attack, hundreds or thousands of participating computers could be involved.

In January, British authorities arrested five Anonymous members in connection with the attacks on Paypal.

Defending its use of such techniques, Anonymous issued a statement, arguing that in a digital age, denying access to a certain entity's website has become a legitimate form of civil protest.

"Just as is the case with traditional forms of protest, we block access to our opponents infrastructure to get our message across," Anonymous said in the release. "Whether or not this infrastructure is located in the real world or in cyberspace seems completely irrelevant to us."

The group — often seen wearing Guy Fawkes masks made famous by the movie V for Vendetta — has previously attacked the Church of Scientology, which it saw as restricting freedom of speech. It also targeted the website godhatesfags.com, which was set up by the Westboro Baptist Church, whose members have protested at the funerals of homosexual soldiers.

More recently, the group has set its sights on HBGary Federal, a major digital security company.

HBGary Federal was targeted when then CEO Aaron Barr attempted to go undercover as an Anonymous member to reveal the identities of its members. The group responded by crippling the security firm's website, making public the company's email archives and demanding Barr step down as CEO.

He formally resigned his position on Feb. 28 but remains outspoken in his opposition to the methods used by Anonymous.