'Dance Moms' Bring Out The Big Guns ... FBI, Cops Investigating 'Mean Girls' Hackers

EXCLUSIVE

1229-dance-moms-fbi-getty-tmz-02The "mean girls" hackers who just hit the "Dance Moms" stars again have something new to fear ... the FBI.

Our "Dance Moms" sources tell us, Monday's hack was the final straw and now some cast members -- including Kelly Hyland, whose two daughters were hacked, contacted the feds. We're told the FBI has actually been on the case since last month, but Monday's hack pushed it to the front burner.

We're told the FBI is not alone ... local law enforcement is also on the case.   

As we reported, the hackers repeatedly got into the cellphones, iClouds, emails and PayPal accounts of Abby Lee Miller, Mackenzie Ziegler and others. The hackers -- whom authorities believe consist of 4 teenage girls -- have been posting phone numbers and other cast info on social media.