SIM
Subscriber Identity Module
A chip identifying a mobile subscriber; targeted by SIM-swapping.
A SIM is the chip that stores the identity and keys authenticating a subscriber to a mobile network, and increasingly appears as an embedded eSIM. It is the target of SIM swapping, where an attacker convinces a carrier to move a victim's number to a new card in order to intercept calls and one time codes. That risk is a key reason SMS based multifactor authentication is considered weaker than app or hardware token methods.
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Looking SIM up is step one. Getting tested on it is step two.
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