Sometime we got annoyed by unknown number but could not find who is calling and where from the call coming.In these case Truecaller is a great help. When we search a new number according to my experience it gives 85% accurate results.Actually truecaller works on maintaining a global database. When we install this app it stores all the contacts saved in the mobile phone. It also maintain its database by collecting data from social networking sites also.In this way truecaller maintain a global database. Sometimes it makes mistake because due to owner of the number has changed but it has maintained its old database. Though most of the cases it gives right result. So this is a nice app. Some says problem of security issues. Simply think only it maintains the contacts database where from the security problem coming.