UK websites are more likely to crash on a Monday morning, not because this is when hackers or viruses are most active, but because this is when developers come in and implement ideas they had over the weekend.

Development staff are now a bigger threat to website uptime than hackers and viruses combined, according to data taken from 70 leading sites over a nine-week period.

'Manic Monday' syndrome often arises when web developers tinker with the site after 'weekend inspiration'.

This results in more faults on a Monday morning than at any other time, said enterprise applications specialist Attenda, which conducted the research.

Neal Gandhi, vice president of product management at Attenda, said: "The quietest time of year for website problems is over Christmas and New Year because the development teams are away, even though it's a busy time for consumer websites.

"Then, as soon as you see the developers logging on again, the trouble starts."

Attenda advises businesses to ensure that the work will have the intended positive effects by putting stringent change control processes in place, such as change management and a test server.

This, along with thorough pre-emptive testing and adequate roll-back provisioning, will ensure that bad code does not take the site down.

"There is a perception that these rules slow down development and cost money, but they don't and you end up with much higher availability," said Gandhi.

"However, you still get managers who don't understand the technology and want changes implemented yesterday. If it goes wrong it's the developer that ends up with egg on the face."