Truecaller is the application that tells us about the unknown no. thats not saved on our phone! this is best concept for the application but their approach is totally wrong!
what this application does is that when any one installs this app on any phones it syncs the contacts from our phone directory to their database . their might our personal data which we do not want to disclose will also be synced!
And if any one searches this no. then the name saved in our directory will appear to them!
Now in recent update they aslo sync the google circles and show the users as shared connections!
Users just install the app but dont know what this app does in background! stay alert to this kind of apps . There I s an app called UNHACK available on playstore just download and check it will show what our apps are stealing our data!