Hundreds of staff at councils, hospitals and schools have been investigated and in some cases sacked for misusing the internet at work.
Many got in trouble for using social networking sites and for posting abusive messages while others resigned or were dismissed for viewing pornography.
A survey by the Yorkshire Post has revealed that teachers and social workers were among those caught in the net.
Private companies are facing similar problems with staff, according to lawyers.
Cases uncovered using the Freedom of Information Act, covering the last five years include:
158 Wakefield Council staff investigated for misusing electronic equipment; two sacked.
Nine cases investigated in Leeds; two staff sacked, one for looking at porn.
32 investigated at Doncaster Council, including eight for comments on Facebook; five sacked, five resigned.
90 investigated at Sheffield hospitals; 11 dismissed.
Two Barnsley teachers sacked; one for accessing porn, the other for derogatory emails about colleagues.
Four West Yorkshire fire service staff warned for sending offensive material.
Seventeen Yorkshire Ambulance Service staff investigated, including 11 for misusing social media sites; one dismissed.
10 investigated at NE Lincs Council; five dismissed.
29 Rotherham Council staff investigated, mostly for inappropriate emails; three resigned.
Public sector organisations have claimed only a small proportion of staff are ignoring the rules.
A spokesman for Sheffield Teaching Hospitals said it had a “zero tolerance” policy and the majority stayed within the rules.
“The excessive use of social networking sites, online shopping or private emails in work time is monitored very carefully and appropriate action taken to ensure NHS time and resources are not being used inappropriately,” he added.
Euan Lawrence, solicitor in employment law at Blacks solicitors in Leeds, is dealing with a rising number of cases.
“We’ve recently assisted employers which have had to deal with employees bringing the employer into disrepute through postings on Twitter or Facebook, sending inappropriate emails to colleagues and customers and viewing pornographic content on their work computer.
“Some employees don’t think twice about sending flirtatious messages internally at work or posting statuses about how much they hate their job. However, these are just some examples of online activity which has resulted in disciplinary hearings or, in certain cases, dismissals.
“Misuse of email, the internet and social media is on the increase and, consequently, many employers are beginning to understand the benefits of implementing guidelines and rules in this area. We recommend to all business clients that they establish policies and practices to help guide employees’ digital usage.
“Online misconduct can not only affect workplace productivity but can also damage the employer’s reputation, breach third party confidentiality obligations or facilitate bullying or discrimination of other employees which, in turn, can expose employers to liability.”
He believes companies should publish a clear policy about online behaviour which “will serve to remind employees that online activity, whether in the workplace or relating to the workplace, is not necessarily private”.
He said: “Employees should be encouraged to adopt a ‘think before you send’ attitude at all times.”