The troubled actor was jailed on Tuesday morning (11Jan11) after reportedly contacting his estranged wife Rachael Kneeland.
Los Angeles officials filed criminal charges against Furlong last year (10) and he pleaded no contest to the violation in November.
At a progress hearing on Tuesday, the City Attorney told the court the actor had violated the restraining order last month (Dec10) by coming within 50 yards of Kneeland.
The restraining order requires him to stay 100 yards from her.
The judge ruled Furlong had violated his probation and the actor was cuffed and taken into custody.
He's being held on $75,000 (£50,000) bail, reports TMZ.com.