Thousands of people in England received spam emails telling them they may have cancer.
Authorities at the National Institute for Health Care and Excellence (NICE) said they were inundated with calls Thursday from concerned patients about the fake diagnosis.
British media reported the email had the subject line "Important blood analysis result."
"We have been sent a sample of your blood analysis for further research. During the complete blood count (CBC) we have revealed that white blood cells is very low, and unfortunately we have a suspicion of a cancer," the email said.
It then asked patients to open and print a file to take to their doctor.
On Twitter, NICE said the move was "pretty low" and it appeared the emails came from someone in Turkey or India.
NICE said it was not hackers because it does not keep health records.
Police are investigating.