The latest move in the investigation into whether Yahoo was in the wrong when it helped Chinese authorities imprison a dissident journalist is proving more than a little painful for the internet giant.

At a hearing in the US House of Representatives, Yahoo executives Jerry Yang and Michael Callahan were branded "moral Pygmies" and told the company gave a "misleading testimony" last year.

Tiananmen blackout

The case centres on Shi Tao, a 39-year-old journalist. In 2004 he forwarded an official Chinese government email demanding that news organisations not cover the 15th anniversary of the Tiananmen Square massacre to a group working for democracy in China .

When officials trying to trace the source of the email asked Tao's email provider, Yahoo China, for his personal details, the US company complied without asking why, resulting in Tao receiving a 10-year prison sentence for forwarding the mail. On top of that, his lawyer was suspended and put under house arrest for seeking to defend him.

Official apology

Representative Tom Lantos denounced the actions taken by Yahoo, saying to Yang and Callahan: "While technologically and financially you are giants, morally you are Pygmies."

Yahoo CEO Yang apologised and said his company would make efforts to secure Tao's release, although he declined to offer financial assistance to the family of the prisoner.