‘I’m a professional cyberstalker' Dave Lee

North America technology reporter Published duration 9 August 2015

image copyright Ken Westin image caption Ken Westin uses advanced techniques to track down suspected thieves

"Stupidity is the best vulnerability. That and greed."

Ken Westin openly, and enthusiastically, calls himself a professional cyberstalker. And foolish people are his target.

He uses some of the tools that are popular with the web's creepiest patrons, hacks used to spy on webcams.

But if you're wondering why he's so proud of it, it's because he's using that technology for good.

He developed a suite of tools that people could willingly install on their technology.

If something is stolen, say, a laptop, the tech would kick in - gathering reams of data that in many cases have secured serious prosecutions.

His work has snared everyone from have-a-go thieves to crime syndicates working across the United States.

He's also adept at piecing together clues left automatically from tech activity, like the raw data hidden in photographs taken on many popular cameras.

His expertise has been used by law enforcement, including those trying to catch people creating and distributing child abuse images.

School robbery

The techniques Westin has used go beyond typical measures like Find My iPhone or other mainstream anti-theft tools.

It also provides a quicker method for the authorities to locate stolen items, offering intricate details instantly, reducing the risk that thieves be able to just move the device miles and miles away.

image copyright Ken Westin image caption In this captured image, more stolen goods were seen in the background

Westin's first significant success was in retrieving a stolen laptop. Using the software, he was able to take a picture of the suspect and tag GPS co-ordinates.

The picture was interesting. In the background - lots of expensive looking gear. When police arrived, they found the owner of a local tattoo parlour. At the property, three stolen laptops, and a host of stuff.

One of the most satisfying results, Westin said, was when they caught up with a gang routinely stealing computers from several schools in Portland, Oregon.

They would work on a rotation basis: Steal machines, wait for them to be replaced, steal again.

They set up computers loaded with the spy software, and left them as bait. Sure enough, they were stolen, and tracked to a Russian gang operating in the area.

Police didn't tell the gang how they'd been tracked down.

image copyright Ken Westin image caption Viktor changed the computer's log-in details to his own, full name

"They arrested six or seven people," explained Westin.

"They got them to think they'd all ratted on each other."

Often, Westin said, thieves come undone due to their own stupidity.

Take Viktor. He stole a laptop, changing the machine's log-in name to his real full name, and then used the machine to upload pictures of his car, complete with number plate.

And then there's the two men who stole a mobile phone that had Westin's software installed. They took pictures of themselves doing drugs, while driving, at 110mph.

Privacy worry

While some of the thieves snared by Westin and police relied on the specially created, and wilfully installed, software - there are other ways to cleverly track down stolen goods.

One of the smartest is Stolen Camera Finder, a web service which examines the EXIF that many cameras, especially high-end models, include in each picture file. It can include the time and location of pictures, as well as the serial number of the camera that took the picture.

So, if your camera is stolen, you can upload a picture you've taken in the past to Stolen Camera Finder, and it will search the internet for other pictures with matching EXIF data.

image copyright Ken Westin image caption One suspect took pictures of their speedometer - at 110mph

If the camera thief has uploaded a picture, you could find a match and some crucial clues to the camera's whereabouts.

This technique is sometimes put to use, Westin said, by authorities trying to find and prosecute those creating child abuse images - seeing if the same camera was used to take any other pictures that might provide more information that could lead to an arrest.

There are, inevitably, privacy concerns with the work Westin carries out.

The nature of the software he created - unnoticeable to the user - means the same techniques could be used for nefarious purposes. Spying on people, for instance, or collecting private data.

But he told me he put measures in place to at least limit that possibility.

Images from a webcam, for instance, can only be taken once every 30 minutes or so. This limits the spying potential if the software is abused.

His argument is that there's software freely available that can do much worse. "Ratting" is a term given to people who hijack people's machines with a view to spying on them - usually through built-in webcams.

Follow Dave Lee on Twitter @DaveLeeBBC