Some antivirus tools can detect Facebook Hacker as dangerous/unsafe application. This is because it's software used to hack Facebook passwords. It's not intended to infect your PC, it's just dangerous because of it's purpose. So if you have antivirus installed, it's recommended to temporary disable it while using Facebook Hacker.
It's also recommended to download Facebook Hacker only from this official website because Facebook Hacker downloaded from other sources could be possibly backdoored and infected.