local ZombieSpawnPoints = {

        Vector( -10744.872070, 8951.499023, 136.031250 ),
        Vector( -10671.409180, 9722.273438, 136.031250 ),
        Vector( -2123.650879, 887.135925, 41.031250 ),
        Vector( -648.224121, 2280.922607, 41.031250 ),
        Vector( -674.037415, 3889.012451, 41.031250 ),
        Vector( 1398.665894, 4111.017578, 41.031250 ),
        Vector( 1391.172729, 1106.842773, 41.031250 ),
        Vector( 1594.428345, -980.007568, 41.031250 ),
        Vector( -220.279266, -877.248230, 73.032227 ),
        Vector( -2124.053711, 851.510925, 41.031250 ),
        Vector( -2145.654053, -1475.522461, 41.031250 ),
        Vector( -3533.449951, -1811.220947, 41.031250 ),
        Vector( -3484.442627, 3512.846680, 41.031250 ),
        Vector( -1141.693115, 4553.960938, 49.031250 ),
        Vector( 541.590210, 852.819275, -86.968750 )
}

local numZombies = 0
local maxZombies = 500

function ZombieSpawns()

     timer.Create( "Respawner", 60, 500, function()

        if ( numZombies < maxZombies ) then

            for k, v in pairs( ZombieSpawnPoints ) do

                    local zombie = ents.Create( "npc_zombie" )
                    zombie:SetPos( v )
                                        zombie:SetCustomCollisionCheck( true )
                    zombie:Spawn()
                    zombie:Activate()

                    numZombies = numZombies + 1

            end

        end

    end )
      timer.Start("Respawner")
end

hook.Add( "ShouldCollide", "ZombieNoCollide", function( ent1, ent2 )

    if ( ent1:GetClass() == "npc_zombie" and ent2:GetClass() == "npc_zombie" ) then

        return false

    end

end )

hook.Add( "InitPostEntity", "StartZombieSpawning", ZombieSpawns )