You’ve just shared your phone number. But what else have you shared? Here are the risks you may never have considered.

You sign up for a loyalty card. You open an account on social media. You sign up for a new online service.  You’re asked to supply your name and your email address - and, more and more often these days, your phone number. 

Our mobile phones are practically extensions of our bodies - of our very selves. They live on or near us 24/7. They hold our most precious memories, our most intimate secrets - from our bank balances to our dating life. They track our movements, our appointments, our connections.

Your phone number is an even more accurate way of identifying you than your own name, say experts. 

And unlike even our physical addresses, our mobile phone numbers rarely change. They follow us faithfully from job to job, house to house - even from country to country.

All of that - in a highly connected world - means your mobile phone number is probably the most powerful piece of personal information you own. It also means that when you give that number out, you're handing out a key to your life.

And if that sounds dramatic - so are the consequences.

The risks

Anyone with access to your phone number and an easily available online public records directory can view an astounding array of information about your life. Your birth date. Your current address. Your past address. The taxes you pay. The names of family members. 

In fact, your phone number is an even more accurate way of identifying you than your own name, says security researcher Emre Tezisci.

Armed with the information your phone number has unlocked, a hacker could:

• Reset passwords for your online accounts by answering security questions like “What is your mother’s maiden name?”
• SIM swap, by tricking your phone carrier into porting your number onto a new SIM card, and proceed to 
• Break into your accounts by receiving an SMS security code
• Con family members into sharing passwords or sending money

But it’s not just hackers who can, and do, take your phone number and run with it. Dodgy marketers can also exploit the access you’ve provided - for example, adding your number to a database that will spam you with promotions.

When is it safe?

Are there situations where sharing your phone number can actually protect you? Absolutely, say cyber security experts. 

For example, the two-factor verification process your bank may use before initiating a transaction, which entails sending an SMS with a one-time-use code. In this case, you are enhancing your security by allowing access to your phone number. 

But with other companies - Facebook, most notably - there have been worrying breaches regarding two-factor verification. And you should know that most tech companies offer alternative verification options that do not rely on SMS. On the whole, these are a safer bet.

Steps you can take

While there is no simple rule to follow, experts recommend thinking twice, and maybe even three times, before sharing your number online. Do the benefits outweigh the potential risks?

Another strategy is to set up a second phone number, using an app like Google Voice or Burner. When in doubt about the people or brands who are wanting your number, supply this “safe” number - not your primary one.