Not all private servers are illegal. Most private lineage2 servers that run on l2j are legal. There are also alot of illegal ones, but I host my own, free and legal. You can check it out at my website www.freelineage2.info or if you want info about other servers, even WoW serves just email me. I will find you ones that are free and legal

TeflonJohn
FreeLineage2 host