The smart lab, report generation, billing and appointment systems of AIIMS were affected.
Delhi's premier All India Institute of medical Sciences might have been subject to a ransomware attack, the hospital has said. All sections of the hospital have been functioning manually since 7 in the morning as the servers started malfunctioning.
In the evening, the hospital, in a statement, said the National Infomatics Centre working to restore the system "has informed that this may be a ransomware attack... (which) will be investigated by the appropriate authorities".
"Measures are being taken to restore the digital services and support is being sought from Indian Computer Emergency Response Team (CERT-In) and National Infomatics Centre," the statement read.
Ransomware is a malicious software designed to deny a user or organisation access to files on their computer. In most cases, the cyberattackers demand a ransom to allow access to the files.
The city's largest referral hospital, which caters to 1.5 million outpatients and 80,000 inpatients every year, has been operating manually since morning, leaving long queues at every department. The worst hit was the registration section, where hundreds queue since dawn to get themselves registered.
Besides, the smart lab, report generation, billing and appointment systems were also affected.
"AIIMS and NIC will take precaution to prevent such future attacks," the hospital said in the statement.
According to AIIMS website, the hospital was established in New Delhi in 1956 as an institution of national importance to serve as a nucleus for the development of excellence in all aspects of the healthcare system in India. The computer facility was launched in a small way in 1978.