The McGill University Health Centre's computer systems are back up and running following a system failure Monday. 

The hospital network said its computer systems went down around 11:30 a.m. The problem was resolved by 7 p.m.  

Hospital officials said they do not believe the computer shutdown resulted from a hack.

The system failure was the biggest the hospital has ever had to deal with, according to Dr. Ewa Sidorowicz. It resulted in cancelled clinical appointments, and diverted ambulances. 

An ambulance ban went into effect right away and patients needing emergency care were diverted to other hospitals. The ban was partially lifted around 5 p.m. in order to admit trauma patients. 

Patient safety was prioritized during the crash, hospital officials said, adding that, while some surgeries were cancelled, there was no indication that the computer outage affected critical care.