A virus attacked the Waikato District Health Board's computer system on Thursday when the system was being upgraded.

Conficker virus infected about 3000 computers across the DHB's network forcing a complete shutdown after the worm was spotted at about 2 am. Microsoft first encountered the virus in November
2008.

Alan Hesketh, the Health Ministry's deputy director general of health information directorate, said the virus attack was believed to be a part of Malware (malicious software) in the digital world.

The Waikato DHB had successful protection against these attacks but its IT system was experiencing an extensive upgrade when the virus got in.

Hesketh said, "some weakness was noticed when they were going through this upgrade."

There were no reports of the Conficker virus attacking other IT systems. To avoid any risk to patients Waikato's system was shut down.

Health Waikato chief operating officer Jan Adams said caution was needed to avoid any possibility of getting re-infected.

The switchboard, emergency department at Waikato Hospital and operation centre were back online last night and elective surgeries, clinics and operating theatres operated normally, DHB spokeswoman Mary Anne Gill said.

Conficker gained access to computers running Microsoft software by exploiting a security hole in the Windows Server service used by Windows 2000, Windows XP, Windows Vista, Windows Server 2003, Windows Server 2008 and Windows 7 Beta.