A quarter of UK companies have dismissed employees for internet misconduct.
And 40% of all complaints came from co-workers, a survey of more than 500 personnel managers found.
A total of 69% of dismissals were for workers surfing pornographic websites, according to the research published on Tuesday.
Nearly three-quarters of firms questioned had dealt with internet misuse, with chat rooms and personal e-mails coming second and third respectively in terms of most frequent complaints.
Warnings issued
Researchers found that more than half of managers preferred to deal with these complaints by having a "quiet word" with workers.
Internet misuse
But 29% favoured using verbal warnings.
The study - carried out for magazine Personnel Today and employee internet management firm Websense - interviewed 544 human resources managers and officers from companies employing an average of 2,500 people.
Jonathan Naylor, a barrister in the employment, pensions and benefits division of law firm Morgan Cole said: "Dismissing an employee for Internet misuse is a substantial cost to the employer."
"While there are the obvious costs of advertising for new hires, recruitment, training and supervision, there are also additional financial burdens caused by the interruption to work patterns, the damage to morale and the negative publicity to the organisation as a result of the dismissal."
Have you or anyone you know been sacked for similar offences? Read your stories below.
I opened a harmless looking e-mail in my inbox just as the office sneak walked past my desk. It left nothing to the imagination and I was duly summoned to be dismissed without notice by the HR Director, keen to show his newly acquired knowledge of internet policy. After I pointed out (through my lawyer) that I am not responsible for what is in my inbox, only my outbox, and the company had therefore failed in its duty to protect its employees from such mails, my lawyers received a prompt apology.
Anon,
UK
At my work a temp got fired for receiving an e-mail that was considered offensive... it showed piercings on African tribeswomen (he was a keen body piercer himself) and as they were not garbed to Western standards it was considered offensive. I personally thought this was pathetic.
Ian Morrison,
UK
I suspect that many people that end up getting sacked for "internet misuse" were probably somehow marked anyway. If someone doesn't quite fit in and the management is looking for an excuse, what better than to make an example of somebody for something that everybody does? I've only ever been asked to look into someone, not to watch out for anyone.
Richard Gray,
UK