CBS Beefs Up Security as 'Big Brother' Fans Try Helping Houseguests

"Big Brother" fans are trying to rig the game by yelling over the show's studio wall to help certain houseguests with outside info ... and now CBS is beefing up security.

Sources with direct knowledge tell TMZ ... several fans have been posting up the last several weeks a stone's throw away from the 'Big Brother' house, using bullhorns to send messages to try and help certain houseguests advance.

Our sources say the fans watch the show and scour the live feeds, so they're aware of cast members' game plans ... and the whole thing is becoming very disruptive.

We're told CBS security and LAPD were initially tasked with keeping an eye out on the fans, but things weren't getting better so CBS recently brought in a private security firm to help.

Our sources say security got into a foot pursuit with a male fan who attempted to scale a studio fence, but the guy ended up getting away after jumping into a getaway car.

BTW ... we're told the folks trying to send messages to houseguests are mostly in their 40s, with no young fans in sight.

With season 22 still in production, our sources say the LAPD is also becoming more visible in the area and keeping a close eye on the area where the fans keep gathering.

We're told there was also a drone scare and a rumor floating around social media that someone was going to hurl a banner over the fence ... but so far the fans on bullhorns are the biggest nuisance.

'BB' has been down this road before ... we're told in past seasons fans resorted to throwing tennis balls inscribed with messages over the fence and onto the studio lot in hopes of reaching contestants.