Labour MP Tom Watson has grilled Rupert Murdoch about covert surveillance techniques by News Corp employees as the company held its first shareholders meeting since the phone-hacking scandal broke.

More than 100 people demonstrated outside the annual meeting at News Corp's Fox Studios in LA, with some holding up signs saying: "Fire the Murdoch Mafia."

Mr Watson asked Mr Murdoch whether he was aware that a person who had left prison was hired by News Corp and hacked into the computer of a former army intelligence officer. Mr Murdoch said he was not aware of it, and board director Viet Dinh said the company would look into the allegation.

"I promise you absolutely that we will stop at nothing to get to the bottom of this and put it right," Mr Murdoch told the MP.

Mr Watson evoked private investigator Glenn Mulcaire, who was jailed in 2007 for eavesdropping on the phones of royal staff, in warning of trouble ahead for the company.

"News Corp is potentially facing a Mulcaire II," Mr Watson said. "You haven't told any of your investors about what is to come."

Mr Watson got up twice and spoke for a few minutes during the 90-minute meeting.

Mr Murdoch faced shareholders with small stakes in his company for the first time since the scandal broke in July. Mr Watson, representing shares owned by the labour group AFL-CIO, used the event to reveal new details of what he claims are covert surveillance techniques by News Corp staff.

The MP has spear-headed a two-and-a-half-year probe into phone-hacking and alleged police bribery at the company's British newspaper unit.

Mr Murdoch and his son James, who is in line to succeed him, were grilled by Mr Watson and other politicians in a Westminster parliamentary committee hearing in late July. Rupert Murdoch said he was ashamed at what happened but declined to take personal blame, and he maintained he was the best person "to clean this up".