A London teenager picked the wrong guy’s laptop to steal during last week’s London riots.

Two days after he found his Apple MacBook Pro had been stolen from his London apartment, IT security specialist Greg Martin was able to track down the alleged thief using Prey, a free, open-source tracking application. Once the thief used Martin’s laptop to surf the Internet, Martin was able to gather the thief’s name, school address, IP address and Facebook ID number.

Martin, a former NASA and FBI employee who wrote about the incident on his blog, was traveling in Luxembourg when the alleged thief finally logged on. He contacted London's Metropolitan Police who were able to arrest Soheil Khalilfar, 18. During the two hours he watched Khalilfar, Martin was able to take photos of the perp with the laptop’s webcam and watch him shop for a Mercedes A Class and view religious revelation videos.

While Martin’s crime-fighting use of tech was praised by many on Twitter (“great story, Idiot theif (sic),” Sebastian Green tweeted), some comments on his blog showed anonymous users were upset with him for giving away security secrets.

“Yes, let's shout out about how Prey is great everytime someone steals a Mac, so that everyone knows about it and is able to avoid it next time,” one poster said. Others took exception to Martin’s self-identification as a hacker.

“Making a monitoring app is trivial—it's a job of a software developer (which I am), not a hacker. Hackers can use any OS and any software they wish to aid their efforts. Stop being tards,” another anonymous reader said.