A study by the Department of Psychology at North Carolina State University has shown that computer users largely ignore pop-up windows that warn of potential danger.

Forty-two students were given computers and exposed to four pop-up windows which warned them that something was wrong with the computer.

One was real and the others varied from warnings of programs executing or terminating, to a black-and-white flashing pop-up that added a browser status bar.

The students were not told the purpose of the experiment, but were under the impression that they were rating medical web pages for clutter. The researchers wanted to see how students dealt with the pop-ups.

Over half simply clicked 'OK' on the pop-up buttons almost automatically. The reaction time varied little for each type of box, suggesting that users were not digesting the contents.

Around 12 per cent of participants said they clicked on the 'OK' button in the pop-up because the box told them to do so, and nearly a quarter admitted that they did this with any pop-up.

Over 40 per cent indicated that they just wanted to get rid of the box as quickly as possible.

Fewer than a quarter actually attempted to close the pop-ups manually, and one in six just dragged the box off the screen and carried on as normal.

The results of the study are not good for operating systems like Windows Vista, which rely heavily on pop-ups to protect users. It also poses a challenge for IT administrators in making sure that staff do not download files from infected sites.