Truecaller functions by crowdsourcing contact books. When a user installs Truecaller, their contact list contributes to the global database. Using an "unlocked" version does not change this dynamic; in fact, it may exacerbate it. A modified app may silently harvest additional data—such as precise GPS location or SMS content—and transmit it to a third-party server controlled by the modder, rather than (or in addition to) Truecaller’s servers.
The most immediate risk is the injection of malware. By installing an APK from a third-party forum (often hosted on file-sharing sites), the user has no guarantee that the code has not been further modified to include trojans, spyware, or keyloggers. A study by the Symantec Security Response has frequently shown that modified popular apps are a primary delivery vector for mobile malware, such as hidden SMS subscription services or ransomware. truec4ller unlocked