He was hired to fix their computers, but police say that Trevor Harwell instead installed spyware software that took candid photos of his clients in various states of undress.

Harwell had been a Macintosh specialist with a Los Angeles-area home computer repair company called Rezitech. That's how he allegedly had the opportunity to install the spy software, called Camcapture, on computers.

While working on repair assignments, the 20-year-old technician secretly set up a complex system that could notify him whenever it was ready to snap a shot using the computer's webcam, according to Sergeant Andrew Goodrich, a spokesman with the Fullerton Police Department in California. "It would let his server know that the victim's machine was on. The server would then notify his smartphone... and then the images were recorded on his home computer," he said.

Police say they've found thousands of images on Harwell's computers and have identified dozens of victims, all of them women in Los Angeles and Orange County. Harwell was arrested Wednesday by Fullerton police.

Harwell was formerly a student at Biola University, a small Christian university in southern California. Many of the victims were Biola students and Harwell may have compromised university systems as well, police said.

Harwell couldn't immediately be reached for comment. Rezitech representatives were unable to immediately comment for this story.

Police were tipped off last year after a Rezitech customer took her computer into an Apple Genius Bar for servicing. It had been popping up weird messages. One of them, designed to look like a Mac OS X system warning, said, "You should fix your internal sensor soon. If unsure what to do, try putting your laptop near hot steam for several minutes to clean the sensor."

The Genius Bar technician found the Camcapture software on this victim's computer and said, "You need to call police," Goodrich said.

She wasn't the only person to get this particular message. Some victims, tricked by the pop-up warning, did take their computers with them into the shower, Goodrich said.

Victims can find the Camcapture software by looking in their /Library/WebServer/Documents folder.

Robert McMillan covers computer security and general technology breaking news for The IDG News Service. Follow Robert on Twitter at @bobmcmillan. Robert's e-mail address is robert_mcmillan@idg.com