Kettering General Hospital has shut down all its external IT systems after the ransomware virus attack across the NHS today.
In a statement published on KGH's website, a spokesman said the move had been taken "in order to maintain patient safety, confidentiality and the functioning of our systems across the county".
The spokesman added: "We would ask that patients do not attend A & E or other emergency services unless it is a real emergency.
"Patients should continue to access other services as they would normally do, but they may not be able to a call in advance as some telephone systems are affected. Not all organisations have functioning land lines at present and other arrangements are being put in place.
"A situation such as this inevitably places a huge impact on all out services and we ask members of the public to only seek medical attention if they really need it.
"Every part of the system will have its own contingency plan which is being implemented. We are not currently planning to cancel scheduled appointments next week, but will continue to keep everyone updated via local media and out own social media channels.
"This is a very difficult situation and we apologise in advance that systems will be slower and will need everyone to work with us to minimise the impact," the statement added.