Hackers disrupted internet connectivity in public healthcare institutions in Singapore this week with distributed denial-of-service (DDoS) attacks, a health technology agency that oversees the institutions said.

Synapxe, which manages operations of 46 public healthcare institutions in Singapore and around 1,400 community partners such as nursing homes and general practitioners, said there’s no evidence that public healthcare or patient data, as well as internal networks, have been compromised.

Disruptions to internet connectivity affecting all public healthcare clusters in Singapore started on Wednesday and lasted for about seven hours.

During that time, services like websites, emails, and productivity tools for staff were inaccessible. DDoS attacks flood websites with junk internet traffic to prevent legitimate users from accessing them.

Users had reported errors when trying to access the websites of some public healthcare institutions, such as Singapore General Hospital, National University Hospital and Tan Tock Seng Hospital, according to local media.

Synapxe said it was able to maintain the work of critical systems needed to provide clinical services at the public healthcare institutions, including access to patient records.

According to the agency, the DDoS attacks on Singapore’s healthcare institutions are continuing, and occasional disruptions in internet services may still occur.

“The public healthcare sector will take this opportunity to review our defenses against DDoS attacks, and learn from the episode to further strengthen our cybersecurity,” Synapxe said.

It is not yet clear who is behind the attacks.