Britney Spears has signed up Krav Maga, the Israeli combat techniques Matt Damon uses in ‘The Bourne Ultimatum,’ after receiving a batch of ‘crazed fan mail.’ Krav Maga is credited for helping agility, toughness, self-esteem and mental awareness.

“She has beefed up security, informed them of such mail. She is doing her best to make a comeback but she is terrified about the negative attention she is getting,” says a Spears expert.

“She realizes she does not have the stamina she used to, after having two kids. She is tired, her body does not work the same. She is putting in overtime into working out strength training, and she’s serious about martial art Krav Maga.”