Three-quarters of staff dismissed for inappropriate internet use were downloading porn in the workplace, according to a survey published yesterday.

Nearly 75% of companies have taken disciplinary action against staff for internet misuse, with a quarter having dismissed workers. Of those, 69% were fired for accessing pornographic websites.

Of the 544 company human resource managers surveyed, 72% said they had been forced to deal with internet misuse. Some 40% of complaints came from co-workers who felt that their colleagues were spending too much time surfing and not enough working.

The research, carried out by the software company Websense and Personnel Today magazine, found that chatrooms (26%) and personal emails (23%) were the next most common causes of internet-related complaints. Racist material, gambling and weapons sites were also frequently mentioned.

More than half of managers preferred to deal with complaints by having a "quiet word" with workers, but around a quarter of cases ended with dismissal.

Internet misuse is relatively new for employers, who have generally treated it as an IT rather than a human resources problem. In the past three years personal internet use in the workplace has almost trebled, with 45% of employees thought to surf during work time.

"Pornography is the category that people find most offensive and is the one most likely to cause the person to get dismissed," said Geoff Haggart of Webwise.

"You might for instance say that only one hour's personal surfing time a day is permitted, and no music can be downloaded until after 6pm.

"Then you can use software to manage that access. If you just ban it altogether you're just going to come up with even more reasons to fire people."

The survey found that managers believed 20 minutes of personal surfing a day was acceptable, even though they were more likely to surf when they should not than staff.

The research showed that staff with their own offices or working alone were more likely to visit inappropriate sites.