Friends and relatives desperately seeking news of loved ones after the Asian tsunami have been plagued by hoax emails saying they are dead.
Messages purportedly from Government officials have been sent to people who placed appeals for information on the Sky News Web site.
Police said they were treating the matter as a "very serious crime" and have launched a full investigation.
A spokesman said: "The Metropolitan Police Service would like to reassure the public that these messages are hoaxes.
"The British Government would not use email to convey news of the death of a loved one."
The hoax emails have all been sent from the same bogus address: [email protected].
They claim to come from the "Foreign Office Bureau" in Thailand and state that the missing person has been confirmed dead.
Anyone receiving such an email has been advised to treat it with the "utmost caution".
If caught the hoaxers could face charges of malicious communication or causing a public nuisance.
"Sky is disgusted at the abuse of this messageboard, designed for friends and relatives caught up in the tsunami disaster,'' the broadcaster said.