A SIM (Subscriber Identity Module) is a smart card or embedded chip that securely stores data identifying a mobile user, allowing devices to authenticate with cellular networks for calls, texts, and data, holding unique info like your IMSI (International Mobile Subscriber Identity) and security keys, acting as your digital passport for carrier services.

SIM swapping

a type of fraud where criminals gain unauthorized control of a victim’s phone number by transferring it to a SIM card they control.