Here's how they seem to do it; they get rather close to their target, swarming around their victim until an opportune moment, when with a simple swipe, they've got their prey.
They make no eye contact, sometimes they ride bikes, sometimes they run, sometimes they attack.
Earphones, cash, handbags, backpacks, iPhones and jewellery - anything that's not protected - is fair game.
Rio's shambolic security set up has been slammed by Australian Olympic chiefs, who say not enough is being done to protect athletes and visitors to events.
The criticism came with fresh revelations criminals are bypassing checkpoints with fake or no accreditation, a bullet struck a media tent and two team officials were robbed at knifepoint.
"The organising committee needs to do more, particularly at security checkpoints," AOC spokesman Mike Tancred told the Daily Telegraph.
"The host nation is responsible for the safety of the 10,500 athletes who are in Rio right now, and it is just not good enough."
Rio is one of the world's most dangerous cities and a massive 85,000 strong security presence was deployed with the intention of keeping visitors safe.
"I went into six venues today. At two of them they did look at my accreditation, one was a cursory glance and three took no look whatsoever," Olympic chief Kitty Chiller told News Corp.
"You know they all smile and say hello when you walk through they are very friendly but they don't actually look at what's hanging around your neck."
