Single instance of C# application

using System;
using System.Windows.Forms;
using System.Diagnostics;

namespace WindowsFormsApplication1
{
	public partial class Form1 : Form
	{
		public Form1()
		{
			InitializeComponent();
		}

		private void button1_Click(object sender, EventArgs e)
		{
			Process[] _process = null;
			_process = Process.GetProcessesByName(Process.GetCurrentProcess().ProcessName);
			if (_process.Length > 1)
			{
				MessageBox.Show("Multiple instancess running...");
			}
			else
			{
				MessageBox.Show("Single instance only....");
			}
		}
	}
}