< script language="javascript" >
function copy() {
    alert("Can't copy the text");
    return false;
}
function paste() {
    alert("can't paste text");
    return false;
}  
< /script >

< asp:TextBox ID="TextBox2" runat="server" Text="hi" oncopy="return copy();" onpaste="return paste();"> < /asp:TextBox >