With　the　rapid　development　of　computer　network　and　information　technology,　the　Internet　has　been　suffering　from　a　variety　of　security　attacks　over　the　past　few　years.　Attacks　have　become　both　numerous　and　complex,　and　the　defender　can　not　understand.　In　order　to　understand　and　defend　against　cyber　attacks,　it　is　necessary　to　understand　the　kind　of　attack.　In　this　paper,　we　study　computer　and　network　attacks,　and　introduce　a　classification　of　them　and　propose　a　cyber　attack　classification　called　DMAT　(Defense-oriented　Multidimensional　Attack　Taxonomy).　We　use　nine　categories　to　describe　the　characteristic　of　the　attack,　which　are　attack　target,　attack　impact,　attack　purpose,　attack　cost,　attack　exploiting,　attack　source,　attack　automation,　attack　loss　and　defense.　The　ninth　category　in　the　DMAT,　classification　by　defense,　is　used　to　provide　the　defender　with　instructions　of　how　to　defense　an　attack.　Compared　to　the　existing　taxonomies,　our　taxonomy　efficiently　classifies　complex　attacks　and　guide　the　defender　to　defense　the　possible　attack.　©　2013　Kavala　Institute　of　Technology.　All　rights　reserved.