Having your name on a mysterious criminal database that leads to your detainment is the stuff of nightmares — but for an increasing number of people in the U.S., it's becoming a reality.

The gang databases responsible are the subject of Sunday's episode of Last Week Tonight, with John Oliver discussing everything from people being flagged as gang members for innocuous posts on social media to outdated databases leading to people being detained years later.

"It is pretty clear that gang databases are way too easy to get on, way too hard to get off, and can turn people's lives upside-down. So what do we do? Well I'd argue we get rid of them. And if you think, 'Well hold on, how will police then stop gang violence?' I say, with police work. They could and should do actual police work focussing on where violence is concentrated, instead of fixating on labels," says Oliver.

"I'm not saying that violence associated with gangs isn't real or isn't a problem. I'm just saying the answer needs to go beyond policing and way beyond these databases."