How to implement a 30 day trial period?

Question

Hello,
I'm trying to implement a 30 day evaluation period for a pure C# WinForms commercial application. The requirements are basically that an uninstall / reinstall should not reset the countdown and it should not be trivial for the user to do it himself. It would also be nice if it were obscured even from detection using SysInternals regmon / filemon software.
I'm thinking of storing the install date somewhere, but where? I tried using isolated storage, but was disappointed to see it just stores as a normal file in the user's Application Data directory.
Certainly this problem has been solved before. Thanks for any ideas...

Answer 1

 in c# this code work for me,
try it 
The Code snippiest is,
In your main Application, add this code to Programm.CS
using SecureApp;
static void Main()
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            string path = @"Software\Tanmay\Protection";
            Secure scr = new Secure();
            bool logic = scr.Algorithm("tanmay", path);
            if(logic ==true)
                Application.Run(new Form1());
Here all the necessary information will save in Registry.
So you must provide a valid path, which will create this dll. 
In this case the password is : tanmay, 
Those two things are provided as,
bool logic
= scr.Algorithm("tanmay", path);
The main code scr.Algorithm(,) is as follows,
public bool Algorithm(String appPassword, String pass)
            globalPath = pass;
            bool chpass = checkPassword(appPassword);
            if (chpass == true) //execute
                return true;
            else
                bool block = blackListCheck();
                if (block == false)
                    string chinstall = checkfirstDate();
                    if (chinstall == "First")
                        firstTime();// installation date
                        DialogResult ds = MessageBox.Show("You
are using trial Pack! Would you Like to Activate it Now!", "Product key", MessageBoxButtons.YesNo, MessageBoxIcon.Information);
                        if (ds == DialogResult.Yes)
                            Form1 f1 = new Form1(appPassword,
globalPath);
                            DialogResult ds1 = f1.ShowDialog();
                            if (ds1 == DialogResult.OK)
                                return true;
                            else
                                return false;
                        else
                            return true;
                    else
                        string status = dayDifPutPresent();
                        if (status == "Error")
                            blackList();
                            DialogResult ds = MessageBox.Show("Application
Can't be loaded, Unauthorized Date Interrupt Occurred! Without activation it can't run! Would you like to activate it?", "Terminate Error-02", MessageBoxButtons.YesNo, MessageBoxIcon.Error);
                            if (ds == DialogResult.Yes)
                                Form1 f1 = new Form1(appPassword,
globalPath);
                                DialogResult ds1
= f1.ShowDialog();
                                if (ds1 == DialogResult.OK)
                                    return true;
                                else
                                    return false;
                            else
                                return false;
                        else if (status
== "Expired")
                            DialogResult ds = MessageBox.Show("The
trial version is now expired! Would you Like to Activate it Now!", "Product key", MessageBoxButtons.YesNo,MessageBoxIcon.Information);
                            if (ds == DialogResult.Yes)
                                Form1 f1 = new Form1(appPassword,
globalPath);
                                DialogResult ds1
= f1.ShowDialog();
                                if (ds1 == DialogResult.OK)
                                    return true;
                                else
                                    return false;
                            else
                                return false;
                        else // execute with how
many day remaining
                            DialogResult ds = MessageBox.Show("You
are using trial Pack, you have " + status + " days left to Activate! Would you Like to Activate it now!", "Product key",MessageBoxButtons.YesNo, MessageBoxIcon.Information);
                            if (ds == DialogResult.Yes)
                                Form1 f1 = new Form1(appPassword,
globalPath);
                                DialogResult ds1
= f1.ShowDialog();
                                if (ds1 == DialogResult.OK)
                                    return true;
                                else
                                    return false;
                            else
                                return true;
                else
                    DialogResult ds = MessageBox.Show("Application
Can't be loaded, Unauthorized Date Interrupt Occurred! Without activation it can't run! Would you like to activate it?", "Terminate Error-01", MessageBoxButtons.YesNo, MessageBoxIcon.Error);
                    if (ds == DialogResult.Yes)
                        Form1 f1 = new Form1(appPassword,
globalPath);
                        DialogResult ds1 = f1.ShowDialog();
                        if (ds1 == DialogResult.OK)
                            return true;
                        else
                            return false;
                    else
                        return false;
                    //return "BlackList";