'The Masked Singer' Security Struggling to Keep Secrets from Swarming Fans

This season of "The Masked Singer" has been plagued with security issues ... and with the season finale approaching, the team is doing everything it can to keep a lid on the show's best-kept secrets.

Our sources say fans and paparazzi have been outside the studio, trying to snap pics through cracks in the fence -- some have even climbed on top of cars to get shots over the barricade.

We're told the studio has seen an increased swarm of people at the entry gate, and it's creating headaches for producers as they try to deal with everyone trying to sneak a peek.

To avoid leaks, the set designers stepped up in a big way ... they worked closely with the 'MS' security team and used set pieces from past performances to build a makeshift barricade outside the studio!

Sounds like lugging giant sets outside and repurposing them as a blockade was an exhausting ordeal, but ended up being worth the effort. Producers were worried that one open sliver would give photogs the shots they were after ... but luckily no pics made it to the light of day.