Fraudsters have been sending messages to users claiming their subscription is ending soon.
The message then tells users to update their payment information, stating that the one-year free trial period has ended.
Action Fraud said the text could trick long-term users of the popular app who may remember paying a 99p fee to use the service.
The original subscription fee was stopped after Facebook bought the company for £11.4bn in 2016.
A spokesman for Action Fraud said: “Whilst late adopters of the service might look at the email below and simply brush it off, long term users will remember paying and could quite easily think the app has gone back to its subscription model and get caught out.”
Last year users were tricked into downloading an exclusive version of Whatsapp "Gold" which infected Android phones with malware.
People are advised to ignore it and not enter their bank details