What motivates individuals to engage in cyberbullying? With the advent and proliferation of social media, forums and q&amp;a sites, there has been a matching increase in the incidents of online-bullying, or 'cyber-bullying, that goes beyond trolling. All too many times, the consequences of this kind of bullying (like any type of bullying) can be tragic.

What is the psychological motivation behind the cyber-bully?  Is it a consequence of them feeling empowered by their apparent anonymity?

I have read the post "Why do teenagers take the internet and cyberbullying so seriously?", but my question is focused on the psychological motivations that the perpetrator of cyberbulling has, not why it is so damaging to the victims.

I am after authoritive (refereed) articles about this.
From my understanding of the problem and my years of experience with the internet since the early days when IRC was popular and web forums were just starting to emerge, I believe I can shed some light on this subject. probably not enough for a full answer but more than just a comment.
I feel that a large part of the problem is the anonymity (or perceived anonymity) as well as the sense of detachment that communication over the internet provides us with. I think that psychologically it is much easier to be critical, mean, cruel and otherwise have a lack of empathy when not dealing with another person face-to-face or verbally. Just as text-based communication does not convey tone of voice to allow us to know when others online are being sarcastic, one can lose the sense of how much one's actions are hurting others when they are cruel online.
With respect to perceived anonymity, it becomes greatly easier to rationalize or entirely forget that one's actions have consequences. It's easy to attack someone online and never have them know who is attacking them. This is demonstrated by a 2005 study done by Qing Li of the University of Calgary (I am unable to find the actual link to the study but have found many places which reference it) that states that 41% of students surveyed did not know the identity of the perpetrators. To me this indices that the anonymity provides a means for humans to rationalize behaviors we otherwise would be ashamed to be associated with.
The paper Cyber bullying:  Clarifying Legal Boundaries for School Supervision in Cyberspace by Shaheen Shariff/McGill University, Canada and Dianne L. Hoff/University of Maine, Orono, USA also draws some very interesting parallels between cyberbullying and the 1954 novel Lord of the Flies by  William Golding, speaking to the roots of cruelty in human nature as well as lack of supervision/perceived anonymity:

Young people in cyber-space lose their inhibitions in the absence of no central power, clear institutional or familial boundaries, or hierarchical structures (Milson &amp; Chu, 2002). As Bandura (1991) explained over a decade ago, physical distance provides a context in which students can ignore or trivialize their misbehavior, as easily as Golding’s boys did on their distant island. In cyber-space this form of disengagement is amplified
Lack of institutional and parental rules in cyber-space have the effect of creating virtual islands similar to the physical islands in Lord of the Flies. The absence of adult supervision allows perpetrators free reign to pick on students who may not fit their definition of “cool” because of their weight, appearance, accent, abilities or disabilities (Shariff and Strong-Wilson, 2005). Cyber-space provides a borderless playground that empowers some students to harass, isolate, insult, exclude and threaten classmates. [...] Without limits and clear codes of conduct, communication in cyber-space (even among adults) can rapidly deteriorate into abuse because of the knowledge and sense of security that comes with the limited possibility of being detected and disciplined.

It also talks about teenage hormones being a driving factor:

Moreover, adolescent hormones rage and influence social relationships as children negotiate social and romantic relationships and become more physically self-conscious, independent, and insecure (Boyd, 2000). Research on dating and harassment practices at the middle school level (Tolman, 2001) shows that peer pressure causes males to engage in increased homophobic bullying of male peers and increased sexual harassment of female peers to establish their manhood. During this confusing stage of adolescent life, the conditions are ripe for bullying to take place. The Internet provides a perfect medium for adolescent anxieties to play themselves out.

I associate it somewhat with the notion by Thomas Hobbes that humans are &quot;warlike&quot;, that by our very nature we are completely self-centered, and that we form societies and governments by giving up some of our selfishness and collectively adhering to social contracts for a greater good. By the nature of online communities often we lose this sense of responsibility to the community and each other, and we are prone to regress to our more basic, warlike state. This is my personal belief; I am still searching for actual references with which I can back this up with.