Override standard close (X) button in a Windows Form

Question

How do I go about changing what happens when a user clicks the close (red X) button in a Windows Forms application (in C#)?

Answer 1

protected override bool ProcessCmdKey(ref Message msg, Keys dataKey)
    {
        if (dataKey == Keys.Escape)
        {
            this.Close();
            //this.Visible = false;
            //Plus clear values from form, if Visible false.
        }
        return base.ProcessCmdKey(ref msg, dataKey);
    }