Internet crime against banks is on the increase, but victims are reluctant to report thefts for fear it will damage their credibility, say police.

According to the National Crime Squad, which last week launched a specialist unit to tackle “cybercrime”, at least four large British internet banks have been attacked, with losses of hundreds of thousands of pounds.

But banks continued to deny the attacks, even when police apprehended the hackers.

The stepping up of police activity comes as Pricewaterhousecoopers (PWC) claimed that internet credit card fraud was growing “at alarming rates”.

The company also estimated that 80% of all serious computer fraud involved employees, with 25% of these involving collusion between an employee and an outsider and 33% involving staff in managerial positions.

PWC says that investment schemes, chain letters, guaranteed loans and offshore trusts “are all examples of frauds that have tricked careless investors into losing millions”.

Other cybercrimes include “denial-of-service” attacks, theft of confidential information, virus infections and email transmission of pornographic, racist or sexist material.

Lawsuits from staff who received pornographic and sexist material cost Microsoft and Chevron more than $2m (£1.4m) in damages.

The company added there were legal problems in dealing with cybercrime, such as area of jurisdiction, lack of legal precedents and the fact that evidence is often difficult to retrieve.