What to do if you receive a call from an unknown international number

The phone rings, you glance at the screen and see an odd prefix: +44, +212, +1809 or something starting with + that you don't recognise. You weren't expecting anything from abroad. The golden rule is simple: don't answer in a rush, don't call back and verify before doing anything. This guide gives you the exact protocol.

Most of these calls are neither an emergency nor an opportunity. They are spam, premium-rate fraud or attempts to get you to take the bait. And the worst thing you can do is react on impulse: pick up and talk, or call back out of curiosity. Let's go step by step.

Why shouldn't you call back?

Calling back is exactly what a good part of these scams are after. The best known is the wangiri (from the Japanese, "one ring and cut"): the phone rings just once from an international number and cuts off before you answer. The idea is that you see the missed call, feel curious and call back. If you do, you dial a premium-rate number abroad, and the bill shoots up by the minute, sometimes simply for connecting.

There are three specific reasons why calling back an unknown international number is a bad idea:

• Direct cost. The number may belong to a premium range in another country. Every second costs money, and that money ends up in the scammer's hands.
• You confirm your number is active. Even if the call is just commercial spam, calling back tells the system on the other end that there's a real person behind that number who picks up. You move onto a "good" list and get more calls.
• You expose yourself to the conversation. If you pick up and talk, you give an opening for social engineering: a pre-recorded voice, a fake operator, a fake relative. The less you say, the less material they have.

The rule, then, is clear: a missed call from an international number you weren't expecting should not be returned. If it were something legitimate and important (a relative travelling, a company you deal with), you have other ways to check it without dialling that number.

What steps do I follow right after receiving it?

Here is the action protocol. You don't have to do everything at once; follow the order and stop as soon as you have your answer.

The key step is number 4: learning to read the prefix. I explain it in the next section.

How do I check which country the prefix comes from?

The international prefix is the block of digits that comes right after the +. Each country has its own. The important thing to understand is that a foreign prefix doesn't automatically mean fraud: it could be a real contact, a company based abroad or a legitimate service. But it is a signal to slow down and check.

To read an international number, mentally separate the prefix from the rest. Some are a single digit, others two or three:

The safest way to identify a prefix is to look it up. Don't trust your memory. And be especially wary of a pattern very typical of fraud: a number that looks like it's from a familiar country (for example, it starts with +1 as if it were from the US) but actually corresponds to a small territory with sky-high rates. That nuance is exactly what international wangiri exploits.

If you want to go deeper into how these codes are read and which ones concentrate the most abuse, there's a dedicated guide at /prefijos, and the article on what to do about a call from an unknown international number you're reading pairs with the one on flash calls and OTP ping calls, where you'll see another variant of the short call that doesn't even want you to call back.

And if I picked up and there was someone on the other end (or a recorded voice)?

It happens, and you're not foolish for it. The protocol changes a little depending on what you hear:

• Silence or a recorded voice. Hang up without saying anything. Many automated operations detect your "Yes?", "Hello?" and use it as confirmation of an active line. Don't answer questions like "Can you hear me?" with a clear "yes".
• Someone claiming to be from your bank, the tax office or a company. Don't give out any data. Hang up and verify by calling the official number yourself, the one on your card, on your latest bill or on the official website. Never the number that called you. This is the basis of verification through a known channel; you have it fully explained in how to verify whether a call or SMS from your bank is real and in how to verify a notification from the tax office or Social Security.
• A supposed distressed relative asking for money. This is one of the most dangerous. With audio pulled from social media, a voice can be cloned with artificial intelligence. If you get a call from an odd number claiming to be your child or your partner in trouble, hang up and call that person directly on their usual number. There's a real case in Spain of a woman who received a call with her husband's cloned voice and discovered it by calling him directly. The data from NoCall and INCIBE tell the story in the article on AI-cloned voices in phone scams.

In every case, the idea is the same: the rush belongs to the scammer, not to you. No legitimate organisation will penalise you for hanging up and calling back through the official channel.

How do I block the number so it stops insisting?

Blocking cuts off repeat calls from that specific number. It's not a magic fix (scammers rotate numbers and spoof the caller ID), but it reduces the noise and gets the day's persistent caller off your back.

How you do it depends on your phone:

• On an iPhone, open the call log, tap the i next to the number and choose "Block this Caller". You can also turn on "Silence Unknown Callers" so that calls from numbers you haven't saved go straight to voicemail. You have the step-by-step in how to block spam calls on iPhone.
• On Android, the exact menu changes depending on the manufacturer (Samsung, Xiaomi, etc.), but the logic is the same: press and hold the number in the log and choose block or mark as spam. You have it broken down by brand in blocking spam calls on Android by manufacturer.
• On a landline or a company switchboard, blocking is handled differently. If international spam reaches your work landline, check blocking numbers on landlines and SME switchboards.

A practical tip: if you get a lot of unwanted international calls, ask your operator whether it can block incoming international calls you don't want. For most private users it's a convenient option if you aren't expecting any contact from abroad.

When is it worth reporting, and to whom?

Blocking protects you. Reporting protects everyone else, and leaves a record. Do it on two levels:

To the community. If you search for the number on /numeros-spam and it doesn't show up, add it yourself with a note about what happened (one ring and hung up, recorded voice, supposed bank...). Every report helps the next person who receives that call to identify it before picking up. You can see what gets reported most and how spam evolves at /tendencias and in the X-ray of phone spam in Spain.

To the authorities, if there was fraud or a serious attempt. The reference channel in Spain is INCIBE, through its cybersecurity helpline 017 (also via WhatsApp on 900 116 117 and through its web forms), which is free and designed precisely for these cases. If you've lost money or given out bank details, contact your bank immediately as well and, if appropriate, file a complaint. You have the full action plan in the guide at /guias.

How do I tell a legitimate international call from a suspicious one?

Not every call from abroad is an attack. This table helps you decide without paranoia:

If most of the signals fall in the right-hand column, treat it as spam or fraud: don't call back, block and report. Learning to read these clues with judgement is what makes the difference; there's a specific guide on how to read a number's risk signals.

In short: your protocol in one sentence

If you get a call from an international number you weren't expecting: don't call back, identify the prefix, verify it through a known channel if it claims to be someone, block it and report it. That sequence saves you money, data and grief.

There's one group that deserves extra attention: older people are the favourite target of these phone scams. If you have vulnerable relatives, share this routine with them and take a look at how to protect older people from phone scams.

Have you received an odd international call? Search for it on /numeros-spam and, if it isn't there, report it. Your report helps the next person recognise it before picking up.