A caller ID spoofing app is an application that can change the phone number displayed on the recipient's device to any number of the caller's choosing. Several paid overseas services have offered the ability to substitute the number that is displayed. With VoIP (IP telephony) the calling side can set the number information in software, which is what makes this rewriting possible.
Legitimate uses do exist. Companies may display their main office number when employees call from personal mobile phones, virtual phone number services may display acquired numbers, and individuals may hide their personal number for privacy. However, misuse for phone scams and harassment has become a serious social problem. Spoofing police or bank numbers to build trust is a standard tactic in bank transfer fraud, and combining it with voice cloning technology enables even more sophisticated scams.
In Japan, the framework for preventing the transmission of someone else's telephone number sits with regulation and with guidelines agreed among carriers. Following the policy on preventing the transmission of a different telephone number, published by the Ministry of Internal Affairs and Communications on 21 April 2008, the Telecommunications Carriers Association (TCA) maintains an operational guideline and a guideline on countermeasures against spoofed caller ID display, as of August 2026. Fraud or threats carried out from behind a spoofed number are punishable as those crimes in their own right. In the United States, the Truth in Caller ID Act of 2009, approved on 22 December 2010, makes caller ID spoofing carried out with intent to defraud, cause harm, or wrongfully obtain anything of value unlawful, and sets a civil forfeiture penalty of up to $10,000 per violation, capped at a total of $1,000,000 for any single act.
As a technical countermeasure, adoption of the STIR/SHAKEN protocol is advancing. This system has originating carriers attach digital signatures to caller IDs, which terminating carriers verify to determine whether the number is legitimate. Rollout among major carriers has advanced in the United States, while Japan relies on the regulation and guidelines described above rather than on signature verification, so the same mechanism is not simply in place there. If you receive a call from a spoofed number, do not trust the displayed number - verify the official contact on the organization's website before calling back. See Caller ID Spoofing - How It Works and How to Spot It for details.