SINGAPORE - More than 1.8 million patients who visited SingHealth's specialist outpatient clinics and polyclinics have received text message notifications from SingHealth on whether their data had been stolen, said SingHealth in a statement on Monday evening (July 23).

These patients had visited SingHealth between May 1, 2015, and July 4 this year.

Remaining patients who did not register their mobile numbers with SingHealth will receive letters informing them about the status of their data this week, said SingHealth.

More than 231,000 patients have also checked on whether they were affected on the Health Buddy mobile app and SingHealth's website.

In the wake of Singapore's most serious cyber attack, SingHealth also alerted the public to suspicious phone calls that have surfaced, reminding patients that they would be informed if their data had been leaked only by SMS or letter.

In a Facebook post on Sunday, it also informed the public on what a genuine SMS notification should look like, after some people said they received fake messages.

SingHealth said that recipients should check that the sender is SingHealth and that the links in the message are www.singhealth.com.sg/cyberattack or bit.ly/cyber-attack18

It stressed that credit card or other financial information would not be asked for.

Those who are unable to do a data check via the Health Buddy mobile app or SingHealth website can call 6326-5555 for assistance, between Mondays and Fridays from 9am to 9pm.