US Army Private Bradley Manning's defense team sought Monday to cast doubt on some of the charges he faces for passing hundreds of thousands of secret government files to WikiLeaks.

At the start of the second week of Manning's trial, the court heard that one software program he is said to have downloaded illicitly while stationed in Iraq was used by everyone in the intelligence cell where he worked.

Manning has admitted sending diplomatic cables and battlefield reports from the wars in Iraq and Afghanistan to WikiLeaks but he denies "aiding the enemy," chiefly Al-Qaeda, a charge that could see him jailed for life if convicted.

Chad Madaras, who worked alongside Manning at Forward Operating Base Hammer in eastern Baghdad, sharing the same computer on alternating shifts, testified that an Internet chat program, known as mIRC, was widely used.

"Everybody had it" on their computers, Madaras, who held the rank of sergeant when he left the army in January this year, said at Manning's court-martial, which is being held at Fort Meade military base in Maryland.

Asked by Manning's civilian defense lawyer if the program had been banned by army commanders, Madaras replied: "No, sir."

The slew of charges that Manning faces, 21 in total, includes counts that he breached army regulations by using unauthorized software for unintended purposes and that he circumvented security systems by acting beyond his authority.

WikiLeaks's decision to publish some of the material it received from Manning caused deep embarrassment to US political leaders and led to his arrest in Iraq in May 2010. He has been held in military detention ever since.

The government argued in the first week of the trial that Manning had set out to leak information almost from the start of his deployment -- he arrived in Iraq in November 2009 -- but the defense disputes this.

The court heard on Monday from Special Agent David Shaver, the prosecution's lead forensic examiner, that Manning had probably first searched the Internet in early December 2009 for information on WikiLeaks and its founder Julian Assange.

Analysis of Manning's computer showed that a slightly later search, on December 29, 2009, relating to "websites that had information pertaining to WikiLeaks," had proven "successful," Shaver said.

He also testified that on March 5 the following year Manning had used a widely-available program, WGet, to download hundreds of reports on detainees being held at the US military prison in Guantanamo Bay, Cuba.

However, under cross-examination from Coombs, Shaver, of the army's Computer Crimes Investigative Unit, admitted that use of WGet had not been forbidden.

Shaver said the 800 or so web searches Manning made included use of the keyword "Farah," relating to a US airstrike in Afghanistan said to have killed 100 civilians, a video of which was passed to WikiLeaks but never published.

Manning, a homosexual, had also done searches relating to gender identity disorder, with which he has struggled, and the military's since renounced "Don't Ask, Don't Tell," policy on gays.