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In an SMS conversation, my friend received a text message within our SMS thread that was clearly not sent from me, and that did not appear in my SMS thread. They took a screenshot and it is in Chinese characters.

Could this only be a SMS spoof, or could it be worse like a SIM Swap Attack?

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If you still have service to your phone, it's unlikely to be a SIM swap attack. Generally, one of the consequences of a SIM swap is that all the services provisioned on your phone (including your phone number) are transferred to the attacker's phone, by the exact same process as those services would be transferred to your new phone when you upgrade. This is the whole point of a SIM swap, because the attacker is trying to intercept any calls or texts which are generated by a multifactor authentication (MFA) scheme to use to impersonate you to that service. More at https://en.wikipedia.org/wiki/SIM_swap_scam.

It's possible, but highly unlikely (unless you are a high-value target of a nation-state-level threat -- and you would know if that were the case), that your SIM could be cloned rather than swapped. Cloning is illegal in the US, and in any case is detectable by carriers who have an incentive to stop such arrangements because they can be used for billing fraud. More at https://en.wikipedia.org/wiki/Phone_cloning.

All of this means that it is likely that it was simply a spoof.

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  • Thanks very much Mike. Pretty sure it was just a spoof but wanted to double check. Appreciate the feedback. – Marc Sep 18 '19 at 17:00
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Maybe... just maybe.. a simple answer is that your friend has a malware on his phone, and the "victim" isn't actually you but him.
I'd suggest you let him know he should comb through his installed apps/plugins, ask if he's installed anything sketchy lately, especially if it reoccurs.

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  • 2
    A rogue app could potentially do it if it has SMS access privilege too – LTPCGO Sep 18 '19 at 22:34

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