Where Do All These Unknown Calls Come From?

If your phone regularly lights up with numbers you've never seen, you're not alone. Unknown calls come from a surprising mix of sources, some harmless, some annoying and some criminal. Understanding where they come from makes it easier to decide which to answer.

Genuine callers using a number you haven't saved

A lot of unknown calls are perfectly legitimate: the GP surgery, a hospital department, a delivery driver, a school, a tradesperson returning your enquiry. Large organisations often call from a different number to the one they publish, and many show as withheld. These callers usually leave a voicemail.

Call centres and auto-diallers

Sales and survey companies use systems that dial many numbers at once and connect whoever answers to the next free agent. If nobody is free, you get silence or a recorded message. That's why answering and hearing nothing is so common.

Your number is on a list

Every time your number is entered into a form, competition or loyalty scheme, it may end up on a marketing list. Some lists are sold on legitimately with your consent (often buried in small print); others are traded illegally.

Data breaches

When a company you've dealt with is hacked, customer details including phone numbers can be leaked and sold. Scammers who buy that data may know your name and which company you use, which makes their calls more convincing.

Random and sequential dialling

Some operations simply dial every number in a range, one after another, to find which ones are in use. Answering, or calling back, tells them yours is live, which can lead to more calls.

Spoofed numbers

The number on your screen may not be the one actually calling. Spoofing lets callers display any number, often a local-looking one or one similar to yours, because you're more likely to answer. Sometimes the displayed number belongs to an innocent person who then gets angry calls back.

Overseas callers

Calls showing an international code may be genuine, but they're also a common source of one-ring scams designed to get you to call an expensive number back.

How to sort them out

• Let unknown calls go to voicemail and listen to any message.
• Look up the number on Who Called Me Check to see the line type, area and what other people say.
• Register with the TPS to cut legitimate sales calls.
• Switch on spam filtering on your phone.
• Report and block numbers that turn out to be nuisance or scam calls.