An IMSI catcher (International Mobile Subscriber Identity) is a telephony eavesdropping device used for intercepting mobile phone traffic and tracking movement of mobile phone users. Essentially a "fake" mobile tower acting between the target mobile phone(s) and the service provider's real towers, it is considered a man-in-the-middle (MITM) attack, and can be detected using tools like SnoopSnitch.[1] IMSI catchers are used in some countries by law enforcement and intelligence agencies, but based upon civil liberty and privacy concerns, their use is illegal in others.[citation needed] Some countries do not even have encrypted phone data traffic (or very weak encryption) rendering an IMSI catcher unnecessary.