CustomProperties safe?

Hunel

Hi,
In my game, 1 score is received for each player killed.
This score value is very important.It should not be changed by the players.

I'm using CustomProperties.
CustomProperties safe? Can it be changed by the players?

Code sample I used:

    ExitGames.Client.Photon.Hashtable props = new ExitGames.Client.Photon.Hashtable();
    void Start()
    {
        props.Add("ArenaKillCount", 0);
        PhotonNetwork.SetPlayerCustomProperties(props);
    }
    void Update()
    {
        .
        .
        PhotonNetwork.SetPlayerCustomProperties( new ExitGames.Client.Photon.Hashtable(){ { "ArenaKillCount", 
        (int)PhotonNetwork.LocalPlayer.CustomProperties["ArenaKillCount"]+1 } } );
        .
        .
    }