US police found more than they bargained for when they did a security sweep of computers at the office of the mayor of the city of Defiance.

According to the Toledo Blade newspaper the systems were packed with so many porn images that it took police more than 20 hours to go through them in search of illegal material.

Sheriff David Westrick said that no illegal material was found, but that it was a startling waste of the public-owned network.

Mayor Fred Schultz and city administrator Roger Reece said the images came from racy email opened "by mistake".

Expressing his embarrassment, the mayor said: "This is a nightmare."

According to Mayor Schultz, porn email started arriving on his laptop a year ago and he accidentally opened a few. But he began receiving hundreds of similar emails over the next few months.

Schultz said there was no way to control the porn spam because the city had no filters for dealing with it.

"I know this doesn't look good. But everyone I know gets these things," Schultz said. "They're a plague."

Reece had also accidentally clicked on pornographic email in an attempt to delete them. "The more you try to click off, the more it seems to come up," he said.

However, the council authorities pointed out that most email solicitations don't contain actual photographs, only links to porn sites.