The spoofing of calling party numbers in international calls terminating in Finland has become a major problem. This global phenomenon became more common in Finland in 2020, and in 2021 the volumes of spoofed calls and their share of the total volume of international call termination increased significantly.
A-numeron väärentäminen suomalaiseksi puhelinnumeroksi on rikollisten laajasti hyödyntämä tekniikka, jonka avulla uhrit saadaan suuremmalla todennäköisyydellä vastaamaan ulkomailta tuleviin huijauspuheluihin. Eräitä tyypillisimpiä tällaisten puhelinhuijausten alalajeja ovat:
Caller ID spoofing or spoofing a calling party number means disguising the number where the call originates as a Finnish number. This technique is widely used by criminals to increase the likelihood of victims answering international scam calls. The following are examples of commonly used fraud schemes:
- technical support scams
- customer support calls from banks
- investment scams
- business service scams (e.g. callers ‘selling’ a company’s own domain name back to the company by threatening to make it available for the company’s competitors).
The Finnish National Bureau of Investigation has reported receiving numerous reports about scam calls like the above in 2020 and 2021. In the cases reported, caller ID spoofing to disguise the calling party number as a Finnish one has been a key element of the scam. The method is commonly used in other countries as well, and it is part of highly organised international crime.
This Recommendation issued by the Finnish Transport and Communications Agency Traficom presents models for analysis and action to detect the following basic cases of caller ID spoofing:
- in international call termination, calls in which the calling party number does not belong to the active Finnish numbering space
- in international call termination, calls in which the calling party number is fraudulently presented as a number belonging to the Finnish numbering space allocated to telecommunications areas in fixed telephone networks or to the numbering space allocated to nationwide subscriber or service numbers
- in international call termination, calls in which the calling party number is fraudulently presented as a number belonging to the numbering space allocated to Finnish mobile networks (mobile number)
- in international call termination, calls in which the field for the calling party number is empty or the calling line identity (CLI) in the field does not comply with the syntax.
When caller ID spoofing has been detected, the call attempt should be addressed by taking the measures specified in this Recommendation.
The models for analysis and action presented in this Recommendation to enable the detection of basic cases of caller ID spoofing only apply to Finnish telephone numbers and Finnish telephone subscriptions. Foreign mobile network subscriber connections roaming in Finnish mobile networks are excluded from the scope of this Recommendation.
This Recommendation has been prepared in cooperation with telecommunications operators in a Traficom working group.