When someone causes another number to come up on your caller ID to hide their identity, it's called spoofing. While spoofing software can be used for illegal purposes, this technology is not always illegal (doctor calling you on their mobile phone, but displaying their office number on caller ID).
What They Can’t Do
It’s illegal for someone to call you with inaccurate or misleading caller ID information to try to defraud or harm you. Telemarketers also can’t block their numbers (and must display business name, if possible).
What You Can Do
While you don’t have much control over who calls your number, you can help to protect yourself from anyone who might want to harm you by
- using apps or services to block unwanted calls
- being aware that the number could be fake (i.e. you're not likely to get an unexpected call from a government agency)
- screening your calls
- hanging up (don't answer any questions or follow any prompts)
- never giving out personal information (especially account numbers, passwords or Social Security numbers) on unexpected calls