Cybercriminals are once again targeting WhatsApp– the most popular messaging service on the planet, with more than two billion users. The nasty scam, which will be familiar to longtime WhatsApp users, leaves people locked out of their accounts. Worse still, this sinister attack also hands full access to your most private messages, contacts list, pictures and videos over to the hackers who can then use these to target more unsuspecting users. This new scam uses an old technique that's been seen in the wild before.

Those tricked will usually receive a message on their phone that appears to have come from a friend or contact already saved on your phone (but be warned – these texts are sent from people who have already been taken in by the scam as the hackers use their contact list to try to tempt more people into falling prey to the scam). Once the hackers know you are willing to respond, they'll target your phone and attempt to gain access to your chat account via WhatsApp's security pin number.

It's a pretty simple scam as whenever you upgrade your smartphone, WhatsApp will ask to verify your identity using your phone number before allowing you to access any chats backed-up to the cloud. It's this six-digit code that hackers need to get their hands on to gain access to your account.To verify the identity of the person trying to log into your WhatsApp, the Facebook-owned firm will send a randomly generated six-digit code in a text message to the phone number that's registered with the account. Of course, this won't go to the hackers, but will end up on your phone.