The term ethical hacking refer to opposite or anti of hacker's.Thereare 2 types of main hacker's one is black hat & another is white hat.first type of hacker's are really hard to nut.they have amazing skills & actually hacking is another name of perfaction at highest level.Black hat hackers are masterpiece but they use there skills against the law(criminal threats,virus spreading,networks destructions,data stealing etc.)where white hat hacker's use there skill to help networks admins to find vulnerability or security holes in there networks by attacking on them.this type of hackers are useful as there aim is to secure networks.these white hats are so call Ethical Hackers.well hacking is a vast term.sometime we think hacker's are criminals,they sit whole day-night in front of pc,they have dangerous face but in actual these all are myths without a 1% truth,the fact about hacker is that hackers are very inteliigent persons in networking ,in programming.most of hackers do hacking just for fun or to show their friends their skills.there is some differance in a virus writer & hacker.where hackers related to networks threats,security the virus writers belongs to higher programming skills in programming,they not related to networks threats like black hat hacker's do.however the destruction cause by virus writer is more harmful.sometime ago love bug virus was created by a 16 years old boy just for fun but this fun ruined over 10 millions pc worldwide & still you can find this virus workling in peoples pc.our aim must be to help security.but the fact again we are also becoming hacker.as to stop a hacker we also must have to be a hacker.hacker & cracker is also a different terms.a cracker is a pure THIEF.his aim only to steal data or thiefting.a cracker is lazy person which uses some 3rd party softwares,trojans,tools,brute-force attacking,dictionary attacking,for steal data.hacker is much much more skilled then a cracker.ths is my personal views in hacking,cracking,virus-coders which I studied till yet.