A spate of hacked Instagram accounts. A $220 million lawsuit against AT&T. A bustling underground crime ring.  They all have roots in an old problem that has lately found new urgency: SIM card swaps, a scam in which hackers steal your mobile identity—and use it to upend your life. At its most basic level, a SIM swap is when someone convinces your carrier to switch your phone number over to a SIM card they own. They’re not doing it for prank call cover, or to rack up long-distance charges.

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