I have never participated in this event. Usually, because I had no idea what it was about, other than avoiding fleet for that week. Last night I took a look at it, and at first glance it appears to be interesting, albeit you had better be prepared with the vaccine or you' definitely get infected.
As with most events, the consist of a series of "daily" & "heroic" quests, with their own rewards and vendors. In this event it happens to be T.H.O.R.N., and no I don't recall what it stands for.
It takes place in a hidden area on Corellia, which you can only access during the event. It also appears to be open to lower levels, so I assume that the mobs scale.