The pair, who split in 2009 after a two year romance, cosied up to each other at Le Baron nightclub in New York earlier in the week.
And fellow clubbers say they “couldn’t get enough of each other.”
A source said: “Lindsay and Sam were whispering and laughing and they left the club holding hands. They didn’t care who saw them and they definitely seem to be back on.
“It was just like the old days, they couldn’t get enough of each other!”
The evening out shows the bisexual actress, 25 – seen leaving her New York hotel yesterday dressed in a sober black suit – has ignored the advice of Judge Stephanie Sautner to stay away from clubs.
In March, the judge finally declared her “endless” probation over, as she completed her punishment for a 2007 DUI charge and the theft of a necklace.
But she warned: “Stop nightclubbing and focus on your work.”
The Mean Girls star has recently landed the role of Elizabeth Taylor in the TV movie, Liz and Dick.
But she was plunged into more legal worries today when police announced they would refer a hit-and-run allegation to prosecutors.
The manager of LA club The Hookah Lounged alleged Lindsay was leaving a nearby club in March, when her car struck him.
He claims she then drove off leaving any info, but the troubled actress denies the charge and says her car was nowhere near him.
The LAPD have now sent the file to the District Attorney, although sources say there is little evidence that the manager is telling the truth.
