Troubleshooters are still trying to flush a virus out of hundreds of hospital computers more than three weeks after it first hit.
The Downadup virus, also known as Conficker B, infected 800 out of the 7,000 PCs at five hospitals in Sheffield, leading to a "small number" of patient appointments being cancelled, according to a spokeswoman for the Sheffield Teaching Hospitals NHS Foundation Trust.
Engineers at the hospitals run by the trust are still clearing up the "last remnants" of the virus, which was first detected on 29 December, she said.
The virus was uncovered at the same time that Microsoft Windows automatic security updates were disabled on PCs supporting operating theatres.
Microsoft released a patch that blocked the vulnerability used by the Downadup virus back in October last year.
David Whitham, informatics director at Sheffield Teaching Hospitals NHS Foundation Trust, said in a statement: "There has been limited impact on patient care."
"The virus has now been contained and our IT team have been working very closely with external antivirus specialists to update PCs and remove the last remnants of the virus from the network to limit the chances of a repeat infection.
"The automatic Microsoft update process had been temporarily disabled following problems with some PCs providing supporting information in theatres.
"This decision was taken by the IT Change Advisory Board to prevent further disruption in theatres."
The latest variation of the Downadup virus has reportedly infected some nine million machines worldwide in recent weeks.
The incident echoes an earlier infection at the Barts and The London NHS Trust, where hospital PCs were struck down by the Mytob worm.