Paladin Antivirus is a fake antivirus (rogue). It's usually installed on the PC from installing programs with an installer that can install additional programs. The program itself claims to have 5 stars, and a "best" value from "PC Pro". Unlike other rogues or antiviruses, Paladin Antivirus has sound effects.
After installing itself on the computer, it claims there is an unauthorized antivirus on the computer, saying that you should remove it, or it would conflict with Paladin Antivirus. The antivirus says that you have malware, when you don't, and tells you to pay for removal of the non-existent malware.