The series was inspired by Martin Scorsese's 2006 film The Departed, which itself was a remake of the Hong Kong film Infernal Affairs. Some critics criticized creator Dimitar Mitovski for adhering too closely to The Departed's plot, considering it an unsuitable model for depicting Bulgarian reality.

Marian Valev, who plays Rosen Gatzov (The Hook), originally auditioned for the role of mafia boss Dzharo before being cast in his eventual role.

During filming of a season 2 scene in which a ZIL 157 truck was supposed to hit Ivo's car on Dzharo's orders, the truck's brakes actually failed and it really crashed into the car with actor Zahary Baharov inside, nearly causing a serious injury.

For the season 5 chase scene involving a van driven by Erol, part of the Hemus motorway was closed for filming; after the van fell off the bridge, the crew rebuilt the guardrails, and to this day that section of guardrail looks different from the rest.

The trolleybus set on fire at the end of season 1, when Dzharo tries to kill Popov in the depot, was a real decommissioned trolleybus that was actually set alight for the scene.

In a season 1 scene where traffic police check Martin's ID, the ID card shown on screen is actually the real personal identity card of actor Ivaylo Zahariev.

The famous line 'Why are you being mean?' delivered by Tihomir Gardev (Big Twin) during a prison fight scene in season 3 was not scripted and was a pure improvisation by actor Kiril Efremov.

Actor Vladimir Vishanski, who played the ruthless Krum, said he was insulted and threatened on the street for a long time by fans of the show after his character killed the fan-favorite Kosam.

The vault heist from season 1 and the cash-in-transit van robbery from season 2 were later replicated almost exactly in real life several years after the episodes aired.

The series received five nominations for the Golden Nymph Award at the 2012 Monte-Carlo Television Festival and won the 'Golden Umbrella' award for Best Series plus awards for best cinematography, best musical score, and most popular series at the 2012 MediaMixx International Festival.

A North American distributor expressed interest in turning Undercover into the world's first 3D television series after BNT sold the international distribution rights to New Films International in 2011.

One episode of the series costs approximately 350,000 BGN to produce.