[Circles](https://attack.mitre.org/software/S0602) reportedly takes advantage of Signaling System 7 (SS7) weaknesses, the protocol suite used to route phone calls, to both track the location of mobile devices and intercept voice calls and SMS messages. It can be connected to a telecommunications company’s infrastructure or purchased as a cloud service. Circles has reportedly been linked to the NSO Group.(Citation: CitizenLab Circles)
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