If you know me, chances are that you asked me for my phone number and I hesitated. Unless we are really, really good friends you probably didn’t get it.

Why?

Robocalls. In other words: telephone spam.

Phones, unlike e.g. email, don’t have a spam filter. It’s also very easy for telemarketers to spoof phone numbers. Most call blocking apps, such as TrueCaller, are totally worthless when you get calls from a fresh and completely random number each and every time.

This means that I’m extremely careful when giving away my phone number.

In today’s world everyone is using a smartphone. Unless you are a Luddite, you’ll probably have “harmless” apps such as WhatsApp installed on it.

These apps work by uploading your phone’s address book to a server and matching contacts using their phone numbers.

The real problem is all the other crap you might have installed on your phone which is uploading the address book to random chinese servers. That address book has my phone number in it.

Guess how my number ended up on that telemarketer’s list? Most likely it was your phone, your poor taste for apps and your knack for clicking “Allow” everywhere. Yup.

Giving away your phone number these days is like writing it on a public toilet’s wall.