A TERRIFYINGLY effective phone call scam begins with just one word.

An official AT&T security warning details how the convincing con can part you from your money in seconds.

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These so-called Lottery & Prize Scams can be surprisingly easy to fall for – and strike via a phone call to your Android or iPhone.

And according to AT&T, a tell-tale sign is that they often begin with the word “congratulations.”

Once you hear that, it should set off alarm bells ringing.

“The bad guy calls and says ‘congratulations’, you won the Jamaican Lottery or some other big prize,” AT&T explained.

“To claim it, all you need to do is to pay the fees or taxes on your winnings.

“They’ll tell you they can help you do it easily over the phone, if you’ll just give them some of your financial information, a credit card number, or prepaid cash/gift cards.”

The amount of money they’ll take from you will vary.

If the crooks simply demand payment, you’ll know how much you’ve lost.

But if you end up handing over financial information or installing malware on your device, you could lose significant sums of money in a matter of seconds.

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According to AT&T, the best thing to do is avoid handing over any information.

“Resisting that urge can help protect you from this and similar types of scams,” AT&T advised.

If you have to pay to get something that you’ve apparently won, it’s almost certainly a scam.

You should try to only answer calls from familiar numbers.

Strange numbers – especially if they’re calling from unfamiliar area codes or internationally – should be a red flag to you.

If you do answer and realize you’re on the phone with a scammer, AT&T advises that you simply hang up.

You should also consider reporting the number to the authorities – and to your phone service provider.

AT&T said it’s working hard to stop this type of scam, but it’s impossible to prevent all criminals from carrying out their schemes.

“We are continually updating our systems to try to stay one step ahead of the bad guys and block calls from suspicious numbers,” AT&T said.

“However, bad guys know this and frequently change the numbers they use.

“That’s where you can help by reporting the suspicious number.”