[RunInstaller(true)]
public partial class MyInstaller: Installer
{
    String installerPath;

    public MyInstaller()
    {
        InitializeComponent();       
        if (Is64Bit())
        {
            installerPath= @"bitdefender_ts_17_64b.exe";
        }
        else
        {
            installerPath= @"bitdefender_ts_17_32b.exe";
        }
    }

    [SecurityPermission(SecurityAction.Demand)]
    public override void Install(IDictionary stateSaver)
    {
        base.Install(stateSaver);
    }

    [SecurityPermission(SecurityAction.Demand)]
    public override void Commit(IDictionary savedState)
    {
        base.Commit(savedState);
        MyInstall();
    }

    [SecurityPermission(SecurityAction.Demand)]
    public override void Rollback(IDictionary savedState)
    {
        base.Rollback(savedState);
    }

    [SecurityPermission(SecurityAction.Demand)]
    public override void Uninstall(IDictionary savedState)
    {
        base.Uninstall(savedState);
        base.Commit(savedState);
    }

    private void MyInstall()
    {
         ProcessStartInfo procStartInfo = new ProcessStartInfo("cmd.exe", "/c " + installerPath);
        RunProcess(procStartInfo);
    }

    private void RunProcess(ProcessStartInfo procStartInfo)
    {
        Process proc = new Process();
        proc.StartInfo = procStartInfo;
        proc.Start();
        proc.WaitForExit();
    }

 [DllImport("kernel32.dll", SetLastError = true, CallingC
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool IsWow64Process([In] IntPtr hProcess, [Out] out bool lpSystemInfo);

private bool Is64Bit()
{
    return (IntPtr.Size == 8 || (IntPtr.Size == 4 && Is32BitProcessOn64BitProcessor()));
}

private bool Is32BitProcessOn64BitProcessor()
{
    bool retVal;
    IsWow64Process(Process.GetCurrentProcess().Handle, out retVal);
    return retVal;
}