Three London Hospitals shut down their computer systems on Tuesday in response to a computer virus infection.

Infection by the Mytob worm sparked the emergency response, involving St Bartholomew's (Barts) the Royal London Hospital in Whitechapel and The London Chest Hospital in Bethnal Green. The three hospitals are members of the Barts and The London NHS Trust.

The Trust's website states that although operating theatres and outpatients departments remain operating as normal, ambulances are being diverted and "some non essential activities have been scaled back". Accident and emergency departments are open only to walk-in patients while technicians work to sort out the mess.

Doctors have resorted to pen and paper backup systems in some cases.

A computer virus has infected the Barts and The London computer system. The Trust’s well rehearsed emergency procedures have been activated to ensure that key clinical systems continue while network access is being established. We have maintained a safe environment for our patients throughout the incident. Manual backup systems are in use and we are in the process of restoring the computer systems with priority being given to the most important areas for maintaining patients services.

A spokesman for the Trust was unable to say when systems would be restored to normal.

It's very rare but not completely unprecedented for malware infections to disrupt the operation of hospitals. The case of a Seattle hospital infected with botnet clients is one of the few that, like Tuesday's London incident, have provoked the roll-out of an emergency response.

The infection at Barts and London Trust was reportedly caused by the Mytob worm, which contains built-in spyware functionality. Mytob spreads by email and has the ability to plant backdoor software on compromised Windows PCs.

Patients with concerns about their appointment are advised to contact the Trust on 0207 943 1335. ®