A secondary teacher in Melbourne who stored sexual images of himself on his laptop computer found himself exposed by a group of students who accessed the files.

Four teenage students are believed to have used the school’s computer network to break into the teacher’s laptop and download the images. Other students who logged on to the network later found a flashing icon in a corner of the screen inviting them to “click me” and when they did so saw a series of files which when opened showed images of the naked teacher.

“I opened three but they were disgusting so I told the teacher,” a student said. “All the kids crowded around me and some saved the pictures on to a disk.”

The teacher resigned from the education department. An investigation was immediately set up to find out how the students managed to bypass security to access the images.

A education department spokesman denied newspaper reports that the images portrayed gay sexual activity.

Under a state government plan, all Victorian teachers are being issued with their own laptop computers which they lease at $3 (pound;1.84) a week. Recipients are required to sign an agreement saying they will not place inappropriate material on them.