username:password:salt

md5(pass + salt)
md5(salt + pass)
md5(md5(pass) + md5(salt))
md5(pass + md5(salt))
md5(md5(...(salt + pass + salt)...))
...
and whatnot.

md5(password.substring(0,4) + salt + password.substring(4,end))

hash(salt . password)

hash(password . salt)