The 'Machete' actress – who had an on/off romance with the DJ until April 2009 – is said to have been in constant contact with her former lover since leaving rehab last month.
A friend of the troubled star told Life and Style magazine: "Lindsay and Sam started speaking as soon as Lindsay got out of rehab. They text constantly. It turned into something more, and they've secretly hooked up."
The DJ regularly visited Lindsay while she was undergoing a drug rehabilitation course at the UCLA Medical Center following her 13-day prison stint for violating her bail conditions of a 2007 conviction for driving under influence.
However, while the 24-year-old actress now claims to be sober, onlookers are said to have spotted Lindsay partying until the small hours at New York's Boom Boom Room on Saturday night (11.09.10) – just 18 days after being released from the rehabilitation facility.
An insider told US Weekly magazine: "It's the same old circle of lying and denials. She's telling everyone she didn't go out. We're like, 'Lindsay, people saw you there!'. It looked like she didn't want to be noticed.
"Everything that she went through seems not to have changed her a bit."