Ashley Tisdale -- Obsessed Fan Arrested for Violating Restraining Order

Ashley Tisdale's obsessed fan just could not stay away from the star ... on social media, at least ... and was arrested yesterday for violating a restraining order, TMZ has learned.

As TMZ first reported, Tisdale was granted a TRO against Nicholas Fiore ... claiming she feared for her life after Fiore threatened to shoot her and her BF, and hammered Tisdale with more than 18,000 tweets since 2012.

Law enforcement sources tell TMZ that Fiore violated the restraining order more than once since it was put in place. We're told the alleged violation was not for personal contact, but rather contact via social media.