Apparently there was some bug on imgur.com that allowed people to upload arbitrary JavaScript appended to the images. imgur.com seems to have acknowledged the issue already[0]. The exploit found was targetting an imageboard called 8chan[1]. There are also a few threads on 4chan about this[2][3][4][5].[0] https://twitter.com/imgur/status/646109824342593536
[1] http://pastebin.com/heYvWu5Y
[2] https://rbt.asia/g/thread/50407085
[3] https://rbt.asia/g/thread/50409306
[4] https://rbt.asia/g/thread/50410681
[5] https://rbt.asia/g/thread/50411692