A survey of 1,685 US businesses has shown that nearly a quarter of workers have to remember 15 or more passwords.

The researchers claim that this is costing money because of the level of support calls and the length of time it takes to get passwords reset.

Nearly one in five of those questioned had to wait an hour or more before regaining access to their systems.

Many users are writing down their passwords to deal with the problem, which can lead to a serious breach of security.

A quarter of users store them on a spreadsheet on their PC, 23 per cent on a PDA, 15 per cent keep a paper record and nearly one in 20 attach their password to the PC with a Post-it note.

"Compliance initiatives have led companies to enforce and strengthen password policies, which has resulted in additional burdens for the end user, such as requiring that employees change passwords more frequently, or use passwords that are very difficult to remember," said Andrew Braunberg, senior analyst at Current Analysis.

"Paradoxically, password policies that are not user-friendly spur risky behaviour that can undermine security. These policies also raise IT help desk costs as companies allocate more resources to password resets."

The survey, sponsored by RSA Security, found that 88 per cent of respondents are frustrated at their company's password policy.