In the last few years, our lives have become more intertwined, due to increased online interactions on social media sites such as Facebook. It is therefore not surprising that social media sites are constant targets for spam, scams and other online attacks. According to Mark Risher, CEO of Impermium(anti-spam software company), spammers own as much as 40% of the accounts on social media sites such as Facebook and Twitter.
Read More: http://www.themaiguard.com/2013/10/we-have-been-invaded-by-email-scammers-on-facebook/

Is not unique to a particular site is common in the internet, all forums and socialnetwork sites.