A frail-looking Manning was seated between two members of his defense team as the hearing got underway after an hour-long closed door hearing between lawyers for both sides.

The defense are set to argue their case at a three-day hearing at the military tribune where Manning, 24, is on trial for allegedly leaking hundreds of thousands of military logs from Iraq and Afghanistan and US diplomatic cables to WikiLeaks while serving as a low-ranking intelligence analyst in Iraq.

In motions filed ahead of the hearing, defense lawyers said the US government used "unconstitutionally vague" or "substantially overbroad" language in eight counts of their indictment, in which Manning is accused of "possession and disclosure of sensitive information."

For two other counts, in which Manning is accused of "having knowingly exceeded authorized access" to a secret Defense Department computer network, defense lawyers said the government failed to state an offense.

Manning, who was formally charged in February, faces a September 21 trial for "aiding the enemy" -- a charge that carries a potential life sentence -- in addition to numerous other counts.

He is being tried at a Fort Meade military base in Maryland, a short distance from the US capital.

"We can confirm that some of the passwords that were compromised correspond to LinkedIn accounts. We are continuing to investigate this situation," LinkedIn's Vicente Silveira said in a blog post.

Silveira said passwords on the compromised accounts were no longer valid, and that those members will receive instructions on how to reset their passwords.

"There will not be any links in these emails. For security reasons, you should never change your password on any website by following a link in an email," he said.

For other members, LinkedIn has implemented "enhanced security" for password protection, he added.

Several security researchers reported the breach, which was posted on a Russian hacker forum.

Graham Cluley of the British security firm Sophos said the hacker posting "does contain, at least in part, LinkedIn passwords."

"Although the data which has been released so far does not include associated email addresses, it is reasonable to assume that such information may be in the hands of the criminals," Cluley said in a blog post.

As a result, Cluley said, "it would seem sensible to suggest to all LinkedIn users that they change their passwords as soon as possible as a precautionary step."

He said users should ensure the password you use is not used on any other websites, and hard to crack.

"If you were using the same passwords on other websites -- make sure to change them too. And never again use the same password on multiple websites," he said.