Many telephone users are not aware that the telephone number displayed for a call isn’t necessarily correct. This is how to protect yourself.
Telephone users have become used to a caller’s number always being displayed for every call they receive. This is a longstanding myth: If a Swiss number is displayed for a call, this call originates in Switzerland and should certainly be considered trustworthy. Many people are not aware though that a number can easily be faked.
Unlike Switzerland, where telephone companies are regulated by BAKOM, users of some foreign, non-regulated telephone networks can transmit any caller number they like. And you can also call into the Swiss landline network this way. All numbers, even if they have potentially been manipulated by an attacker, are passed on unchecked and displayed on your telephone display. The use of faked Swiss telephone numbers is a common practice used by criminals to build up trust in users. In addition, there are also some call centres with Swiss numbers actually operating abroad (source: NCSC).
Protect yourself by:
- immediately terminating any unsolicited calls by purported Microsoft, other IT support company or financial institution employees.
- never relying on a number shown on your telephone display to be actually correct.
- never disclosing any personal data such as passwords or credit card details to any other person.
- always calling the official Microsoft or other IT support company’s official telephone number.
- only ever contacting your financial institution via their official telephone number, which can for instance be found on your account statements.
Further information can be found in our article on “Fraudulent support calls».