The Answer to "How Did They Get My Number?"
Have you ever taken a sales call from a number you did not recognise and wondered how on earth they got hold of your number? Phone numbers make their way out into the world through all sorts of routes, without you ever noticing. This article walks through the five main routes by which a number gets out, and what you can do about each one.
Route 1: You Handed It Over When You Signed Up
When you enter your phone number for online shopping, an app membership or a loyalty card application, it can end up being used for that company's marketing. If the terms of service say something like "we may use this to tell you about related services", the sales call is entirely legal.
The cases that deserve the most caution are prize draws and giveaway campaigns. Enter your phone number because an advert promising a luxury prize caught your eye, and that number may be added to a telemarketing list. The more free a service or campaign appears to be, the more often collecting personal information is its real purpose.
What to do: if the phone number field is optional, leave it empty. Check the "purpose of use of personal information" in the terms of service. Think twice before entering a prize draw or campaign.
Route 2: Leaked to List Brokers
Customer data held by a company is sometimes sold on to list brokers. The brokers sell lists of phone numbers to sales companies, which use them for cold calls. Japan's Act on the Protection of Personal Information prohibits providing data to a third party without the person's consent as a general rule, but there are cases where the data is traded illegally all the same.
The lists that brokers deal in sometimes carry attributes attached to each entry: age, gender, occupation, income bracket and so on. A list filtered by conditions such as "men in their thirties earning over five million yen" is then sold to companies selling property investments or insurance. If the sales calls you receive happen to match your own profile, there is a good chance your number leaked through a list broker.
What to do: if you get a suspicious sales call, ask "where did you obtain my number?" Under the Act on the Protection of Personal Information you have the right to demand an explanation of the purpose of use and how the data was acquired. An operator who refuses to answer is very likely acting illegally.
Route 3: Random Dialling
There is a technique called random dialling, in which numbers are dialled automatically in sequence. The system works its way through 090-1234-0001, 090-1234-0002 and so on, so your number simply came up by chance. It is often combined with robocalls (automated voice calls), and only the numbers that answer are added to a list as "live numbers".
Random dialling is used especially heavily in the one-ring scam, where the phone rings once and is then cut off to lure you into calling back. Call back and you may be connected to a premium-rate information service, or questioned for your personal details. Our article on the dangers of the one-ring scam is worth reading alongside this one.
What to do: if you do not answer, there is a good chance you will be dropped from the list. Not calling back is the important part. When a call comes in from a number you do not know, search for it on this site first and then decide. Our guide to handling calls from numbers you do not recognise also helps.
Route 4: Public Information on Social Media and the Web
Have you ever put your phone number in a social media profile, a blog or a message board post? Once a number has been published online it gets indexed by search engines and stays there almost permanently.
The same applies if you write your phone number in the trading messages on a flea-market app or an auction site: the other party now knows it. If that person has bad intentions, they may sell the number on to a list broker. And when a company website lists a direct number for a member of staff, that number can become a target for sales calls.
What to do: search for your own number on Google and check whether it appears anywhere you did not intend. Remove your phone number from social media profiles. Do not exchange phone numbers directly on flea-market apps.
Route 5: A Data Breach
This is the case where a company suffers a cyberattack and customer data is exposed. Leaked data is bought and sold on the dark web and ends up in the hands of fraud groups and sales companies. There is nothing you can do to prevent it yourself, so the important thing is to keep the damage as small as possible.
Large-scale data breaches happen practically every year. If any service where you have registered a phone number is attacked - an online shop, a game service, a financial institution, a medical institution - your number is at risk of exposure. Leaked numbers are sometimes abused as target lists for phone scams. Understanding the risks of caller ID spoofing as well will make you better equipped to deal with a suspicious call.
What to do: keep an eye on data breach news for the services you use. Change your password as soon as a breach comes to light. Use a service such as "Have I Been Pwned" to check whether your email address appears in leaked data.
What You Can Still Do After Your Number Has Got Out
Even if your number has already reached the outside world, there are ways to keep the damage to a minimum.
- Make use of call blocking: when a nuisance call comes in, add that number to your block list there and then
- Install a nuisance call app: it blocks known nuisance numbers automatically
- Use your carrier's nuisance call service: blocking at the network level is the most reliable approach
- Tell sales callers clearly not to call you again: under the Act on Specified Commercial Transactions, soliciting again after you have refused is prohibited
- Consider changing your number: if the nuisance calls are truly relentless, changing your number is an option of last resort. Be aware, though, that registering the new number with the same services can leak it all over again
Steps You Can Take to Cut Down Nuisance Calls
- Give out your phone number only where it is genuinely necessary
- Install a spam call filter app
- Do not answer numbers you do not know (let them go to voicemail)
- Tell sales callers clearly not to call you again
- Cancel memberships for services you no longer use
- Avoid casually entering your number on prize draw and survey sites
Summary
When a stranger calls you, the cause is one of these: a service registration, a list broker, random dialling, publication on the internet, or a data breach. The best defences are to give out your phone number as little as possible and not to answer numbers you do not know. If your number has already got out, use call blocking and a nuisance call app to keep the damage to a minimum.