The HSE will keep its computer network disconnected from outside communications until Wednesday, despite confirming that ransomware found in the system was not related to the current global attack.
Yesterday afternoon, the HSE also confirmed that nearly all the 1,200 servers that were rebooted to allow an anti-virus update to take effect were back online.
The PSNI has said it is working with partners in government and other agencies to "mitigate any risk to computer networks in Northern Ireland".
A spokesperson for the Department of Health said it was not aware of any "similar incidents at this time" in healthcare organisations in Northern Ireland.
"We have been lucky in that we have been upgrading our computers and hardware, particularly in the last few years".
Any organisations who believe they may be victims of cyber-attack are urged to contact to the police immediately at 101 or via the Cyber Crime Reporting Portal on the PSNI Website or alternatively through Action Fraud 0300 1232040.
The organisation's thought to have targeted Sony Pictures in 2014.
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The same virus may have infiltrated systems in NI, but not yet been activated, said the PSNI.
More than 200,000 computer systems in almost 100 countries have been infected with the so-called WannaCry ransomware since Friday.
The malware has caused severe disruption to health services, industry, transport, academia and law enforcement around the world.
Our version of the NHS, the HSE has been very proactive to ensure that it's business as usual for patients and all HSE employees ensuring that we don't face the issues that the NHS are facing.
"As people return to work after the weekend, many will have unopened, potentially infected emails in their inboxes, or their systems may already be infected and are waiting to activate", Mr Grant added.
The HSE cut off its network from external communications as a precaution, on Friday.
But HSE chief information officer Richard Corbridge said the impact on patients is unlikely to be significant because email is rarely used to communicate with patients.
It meant nobody inside the HSE could receive emails from outside or access the internet or external based platforms.