The Harris Federation was the target of a large-scale cyber attack over the weekend.
Although its schools remained open today, the federation confirmed its servers had been severely impacted and described it as a ‘particularly vicious attack’.
In a statement, a Harris Federation spokesperson said: “A ransomware attack means that cyber-criminals have accessed our IT systems and encrypted, or hidden, their contents.
“We are at least the fourth multi academy trust to have been targeted in March. The attack came to light on Saturday, March 27, and we have been working through the weekend to begin resolving it.
“This is a highly sophisticated attack that will have a significant impact on our academies but it will take time to uncover the exact details of what has or has not happened, and to resolve.
“In addition to using the services of a specialised firm of cyber technology consultants, we are working closely with the National Crime Agency and the National Cyber Security Centre.
“Harris academies are open today and we will endeavour to keep them open until the end of term as specified in the table below.
“As a precaution we have temporarily disabled our email system. Our telephone systems, which run on the internet, have also been disabled but each academy switchboard has been diverted to a mobile telephone.
“Switchboard services are therefore very limited and we would ask that you temporarily avoid telephoning us or any Harris academy other than to report absence or in emergencies.
“Where pupils have Harris Federation devices, these have been disabled as a precaution and cannot currently be used.
“We know that some families will have important individual concerns around data and that in these cases you will want to know more about the nature of the attack.
“Because we do not want to risk providing incorrect information, we will communicate further once we have clarity and liaise as appropriate with the Information Commissioner’s Office.”
The NCSC had issued a warning on March 23 about cyber attacks targeting the education sector.