Socks4 vs Socks5
SOCKS is an Internet protocol that allows client-server applications to transparently use the services of a network firewall. SOCKS is an abbreviation for SOCKetS
SOCKS proxy transfers all data from a client to a server, nothing adding from itself. Therefore anonymity of this type of proxy servers is really absolute.
There are two major versions of SOCKS protocol SOCKS4 and SOCKS5. The major difference between them is that SOCKS5 proxies support UDP, extends the framework to include provisions for generalized strong authentication schemes, and extends the addressing scheme to encompass domain-name and V6 IP addresses.