The attacker, who was taken away by police, apparently struck Murdoch with a paper plate of shaving foam and shouted, "Greedy," the BBC reported.
Murdoch's wife, Wendi, seated behind him, instantly rose to defend her 80-year-old husband.
Testimony by Murdoch and his son, James, resumed after a few minutes.
The Murdochs apologized for their subordinates' phone-hacking but denied direct knowledge.
Testifying before a House of Commons committee, the media titan called it "the most humble day in my life," the BBC reported.
James Murdoch called the scandal that brought down their News of the World tabloid a "matter of huge and sincere regret."
Rupert Murdoch said he works 10 to 12 hours daily and "I cannot tell you the multitude of issues I handle." The News of the World was "small" in the scheme of his work.
He also denied any "willful blindness" by management to the illegal eavesdropping.
Murdoch also voiced regret that the scandal had ended his friendship with former Prime Minister Gordon Brown, who bitterly attacked News Corp. last week for invading his family's privacy.
Throughout the questioning, the son took center stage answering MPs' questions, his father looking frail and sometimes out of touch beside him.
Media committee Chairman John Whittingdale told The Daily Telegraph, "The reason we have asked James Murdoch in particular is that he has publicly stated that we [Parliament] have been misled. We want to know who misled us."
Rebekah Brooks, a former editor of the News of the World and chief executive officer of News International, the British unit of Murdoch's media empire, is scheduled to testify after the Murdochs. She was arrested Friday.
Earlier Tuesday, another Commons committee questioned a top Scotland Yard officer who quit Monday amid the scandal.
John Yates, former assistant chief constable at the London Metropolitan Police, said he resigned because the situation surrounding the mushrooming phone-hacking scandal was a "distraction" to his duties in homeland security matters.
"I firmly believe I've done nothing wrong," he told panel. "My conscience is clear."
Members quizzed Yates about his role in the hiring of former News of the World deputy editor Neil Wallis for a public relations position. He said he received "categorical assurances" that Wallis wasn't involved in phone-hacking allegations at the defunct tabloid and wouldn't embarrass the department.
The scandal has reached the administration of Prime Minister David Cameron because one of the former editors arrested in the case, Andy Coulson, was Cameron's communications director.
The two committee hearings come as police investigate the unexplained death of the News Corp. phone-hacking whistle-blower.
Sean Hoare, 47, who accused Coulson of being part of the illegal activity, was discovered dead at his home days after he made a series of fresh allegations against former News of the World executives, police said.
His death was termed "unexplained" by police, who said they did not immediately suspect foul play.
Cameron cut short a trade mission to Africa to return to London to address the phone-hacking crisis and make a statement before Parliament, his spokesman has said. He was expected to appear before the House of Commons in an emergency session Wednesday to discuss the scandal.
The New York Times reported evidence indicates News International paid hefty sums to people who threatened legal action, on condition of silence. Reporters and editors were also paid to be silent, even after they were fired or arrested for hacking.
Among other things, the phone-hacking scandal has led to the arrests of at least nine people associated with the News of the World, the resignations of Met Police Chief Paul Stephenson and Yates, prompted Murdoch to withdraw his bid to take over British Sky Broadcasting, resulted in the resignation of Les Hinton, chief executive officer of Dow Jones, another News Corp. property, and led to the shuttering of News of the World. In addition, the FBI said it was investigating allegations News Corp. reporters tried to hack into voicemail accounts of victims of the Sept. 11, 2001, terrorist attacks on the United States.