I need help identifying a bug
This looks like an immature passionvine hopper (Scolypopa australis).  They are informally known as fluffy bums.



Source: http://ketenewplymouth.peoplesnetworknz.info/friends_of_te_henui/images/show/1486-nymphs-fluffy-bums-scolypopa-australis

This is am image of the adult stage from the Encyclopedia of Life site:



More information can be found at the Encyclopedia of Life link above.  It appears that their distribution may be only in Australia and New Zealand and I'm not sure where this photo was taken so take this information into consideration.