Why not every mobile number is trustworthy 

How do telephone fraudsters currently operate?

Your mobile rings and a Swiss number appears on the display. However, the caller is actually based abroad and has manipulated the telephone number. This is known as number spoofing.

"This is made possible through special software," says Jens Kaessner, Head of the Networks and Services Security Section at the Federal Office of Communications. Fraudsters also use information from social media channels to create an impression of familiarity during the conversation. Artificial intelligence can additionally imitate the voices of acquaintances or friends.

What is the aim of the fraudsters?

The callers want money. They put their victims under pressure and encourage them to act quickly by pretending to be a relative in distress, the police or another authority.

Sometimes they claim that a bail payment is required for family members, while other times they might mention a horrendous medical bill – supposedly a matter of life and death. Through skilful deception, they coax out passwords and banking details and thus gain access to the relevant accounts.

Are the perpetrators prosecuted?

Legally speaking, such calls are considered fraud. They are punishable by fines or imprisonment. However, as the perpetrators are usually based abroad and cover their tracks, they are rarely caught.

What are telephone providers doing to combat spoofing?

Telephone providers are obliged to combat spoofing. Swisscom – whose network is also used by Migros Mobile – and Sunrise have already activated their own filters against unwanted advertising calls.

From 2026 onwards, calls with a falsified Swiss number must be marked across all networks if the providers recognise the fake number. "The person receiving the call will then see 'Anonymous' or no phone number at all on the display. In very clear cases, the phone will not ring at all," says Jens Kaessner.

How can I protect myself?

If you don't recognise a number, it's best not to answer the call at all. Anybody calling for a legitimate reason can leave a voicemail. If you do answer, you should never disclose any sensitive data.

Caution is advised if psychological pressure is being applied. In such cases, it is best to hang up and then report the call to the telephone provider or the National Cyber Security Centre (NCSC) here.