Jon Gosselin used his computer skills to hack into his wife Kate‘s e-mail, online bank accounts and cell phone, and he smoked marijuana at the family home while watching their kids!

Those blockbuster charges are being leveled against the former star of Jon & Kate Plus 8 by his ex-girlfriend and family baby sitter in an exclusive ENQUIRER interview.

Stephanie Santoro also reveals that Jon plans to demand alimony from Kate, and says he caught on to his estranged wife’s affair with her married bodyguard Steve Neild.

Stephanie, a single mom and aspiring model, got to know Jon while she was working as a cocktail waitress at his regular hangout, Legends nightclub near the Gosselin family estate in Wernersville, Pa.

"Jon told me that he hacked into pretty much everything of Kate’s," Stephanie, 24, told The ENQUIRER. "He had access to her online banking, and he put a trace on every single one of her e-mails.

"Anytime she’d get an e-mail or send one, he’d get a copy of it. Besides that, he knows every single thing she does online, and every text message she gets or receives."

Computer savvy Jon – who once worked as an information technology specialist for the state of Pennsylvania – also claimed to have bugged Kate’s cell phone, said Santoro.

 "Every time Kate used her phone, Jon would know who she was talking to, and what they were saying. He always bragged that he had access to everything in Kate’s life, and that he was going to use it against her," said Stephanie.

Things like THAT help when you’re having a nasty divorce AND cleaning out a bank account!

For the full story and details of Jon’s big brother operation AND  pot smoking while minding the kids pick up the new ENQUIRER – on sale now!