University College London has been hit by a “major” ransomware attack which brought down its shared drives and student management system.

The attack has also led to a number of hospital trusts suspending their email servers as a precautionary measure, in an attempt to prevent the repetition of last month’s damaging WannaCry epidemic.

UCL first reported problems at 5pm on Wednesday afternoon. It believes a phishing email, sent around midday, resulted in the ransomware gaining a foothold on its servers, where it began spreading through the university’s N (network) and S (shared) drives. By 7pm, it had restricted access to those drives, and they are currently available in read-only mode for students and staff.

University College London Hospitals, an NHS trust closely associated with the university, did not report any problems with ransomware, but some hospitals decided to suspend their NHS email systems anyway, as a precautionary measure to prevent a new outbreak.

Barts Health NHS Trust, the largest NHS trust in the UK, was one that closed its mail server: due to its close links with UCLH, the trust “temporarily shut emails down to make sure nothing spread”, according to a spokesperson. East and North Herts NHS Trust similarly said it closed its NHS mail server as a “preventative measure, because we’ve been warned by other hospitals to do so”.

It’s not yet clear what specific strain of ransomware hit UCL, but the university is warning that it may be a “zero-day” attack – one not seen in the wild before – due to the fact that it was not picked up by its antivirus software. The attack began on the same day Microsoft released an extremely rare security update for Windows XP and Windows Vista, warning of WannaCry-style attacks in the future using one of 16 different critical vulnerabilities.