The PSNI has said it is working with partners in government and other agencies to “mitigate any risk to computer networks in Northern Ireland”.
It follows Friday’s cyber-attack which affected more than 200,000 victims in 150 countries.
Det Ch Insp Douglas Grant said no incidents have been reported in Northern Ireland yet.
However, he said the PSNI “cannot rule out the possibility that local systems may be vulnerable”.
“As people return to work tomorrow 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.
“It is of the utmost importance that individuals and organisations act to ensure the integrity of our local cyber networks and take appropriate action to reduce the threat posed by cyber criminals.”
The virus took control of users’ files, demanding payments; Russia and the UK were among the worst-hit countries.
Experts say another attack could be imminent and have warned people to ensure their security is up to date.
The ransomware, which locked users’ files and demanded payment to allow access, spread to 150 countries, including Spain, Russia, the US and China.
In England, 48 trusts reported problems at hospitals, GP surgeries or pharmacies and 13 NHS organisations in Scotland were also affected.
In the Republic of Ireland, there has been one reported infection in a system at a small voluntary healthcare facility in Wexford.
Its computers, which were not connected to the Health Service Executive (HSE) network, have been isolated.
The HSE cut off its network from external communications as a precaution, on Friday.
The Police Service of Northern Ireland (PSNI) said its cyber crime centre would continue to actively participate “in the national co-ordinated response to this attack and we would encourage all local businesses and public services to take immediate steps to protect their systems and reduce their vulnerability”.
“We would also recommend that businesses and industries join the local Cyber Information Sharing Partnership (CISP) so they can receive the most up to date threat and mitigation information to help protect their cyber security,” it added.
The PSNI said further information is available via the National Cyber Security Centre and appealed to anyone who believes they may be victims of cyber-attack to contact them.
The National Cyber Security Centre has said more ransomware cases may come to light on Monday, “possibly at a significant scale”.
Ransomware attacks are “some of the most immediately damaging forms of cyber-attack”, it said, and advised companies to:
- Keep your organisation’s security software patches up to date
- Use proper anti-virus software services
- Back up the data that matters to you, because you can’t be held to ransom for data you hold somewhere else