A "SIM sent a text message" alert has started appearing at random ever since I replaced my SIM card after leaving the old one abroad. It opens as a full-screen prompt with options such as "Cancel" or "Accept," and sometimes disappears by itself. Whenever it appears, my phone briefly loses all signal before reconnecting. Is this a normal carrier or SIM Toolkit message, or could it indicate that my phone has been hacked? I'm also concerned because I noticed an unauthorized credit-card transaction recently.
2 Answers
That sounds like a flash SMS, also called a class 0 SMS. It appears immediately as a full-screen alert instead of sitting in the regular Messages app. These messages are generally sent by the wireless provider or a carrier service on the SIM, and the provider may be the only one able to disable them. Contact the carrier and ask them to check the SIM Toolkit or flash-SMS settings.
This is probably being triggered by an application built into the SIM, commonly called SIM Toolkit. Those carrier services can perform background tasks and send or receive SMS messages, and the phone may display a warning when that happens. The brief loss of signal could simply be the SIM or network re-registering. This behavior by itself doesn’t suggest that the phone has been hacked; the SIM’s built-in software is normally controlled by the mobile carrier.
That makes sense. The alert is full-screen with “Cancel” and “Accept,” and the signal drops to zero briefly before returning. I’ve been canceling it whenever it appears.
Yes, it is exactly that kind of full-screen prompt. I’ll ask my carrier to check whether one of its SIM services is generating it.