A Norfolk-based veterinary firm with more than 500 locations worldwide has suffered "considerable disruption" following a cyber attack. 

CVS Group, which employs more than 9,000 staff and has its headquarters in Diss, said the attack involved "unauthorised access" to its IT systems over the last week. 

To limit the impact, CVS temporarily shut down the systems which disrupted its UK network but it was successful in stopping the hackers from gaining further access.

Specialist third-party consultants are investigating the incident and the group has also informed authorities such as the Information Commissioner's Office "due to the risk of malicious access to personal information".

"Through the efforts of our colleagues, we have continued to provide our usual high levels of clinical care to clients and patients at the majority of our practices," CVS said.

"IT services to our practices and business functions have now been securely restored across the majority of the estate; however, due to the increased levels of security and monitoring, some systems are not working as efficiently as previously and this is likely to result in an ongoing operational impact."

The London-listed company said the security response to the attack "is likely to have an impact on operations for several weeks".