How to Kill A Session or Session ID (ASP.NET/C#)

Question

The Abandon method should work (MSDN):

Session.Abandon();

If you want to remove a specific item from the session use (MSDN):

Session.Remove("YourItem");

EDIT: If you just want to clear a value you can do:

Session["YourItem"] = null;

If you want to clear all keys do:

Session.Clear();

If none of these are working for you then something fishy is going on. I would check to see where you are assigning the value and verify that it is not getting reassigned after you clear the value.

Simple check do:

Session["YourKey"] = "Test";  // creates the key
Session.Remove("YourKey");    // removes the key
bool gone = (Session["YourKey"] == null);   // tests that the remove worked

It is also a good idea to instruct the client browser to clear session id cookie value.

Session.Clear();
Session.Abandon();
Response.Cookies["ASP.NET_SessionId"].Value = string.Empty;
Response.Cookies["ASP.NET_SessionId"].Expires = DateTime.Now.AddMonths(-10);

Session.Abandon()

This marks the session as Abandoned, but the session won't actually be Abandoned at that moment, the request has to complete first.

From what I tested:

Session.Abandon(); // Does nothing
Session.Clear();   // Removes the data contained in the session

Example:
001: Session["test"] = "test";
002: Session.Abandon();
003: Print(Session["test"]); // Outputs: "test"

Session.Abandon does only set a boolean flag in the session-object to true. The calling web-server may react to that or not, but there is NO immediate action caused by ASP. (I checked that myself with the .net-Reflector)

In fact, you can continue working with the old session, by hitting the browser's back button once, and continue browsing across the website normally.

So, to conclude this: Use Session.Clear() and save frustration.

Remark: I've tested this behaviour on the ASP.net development server. The actual IIS may behave differently.

Session.Abandon() this will destroy the data.

Note, this won't necessarily truly remove the session token from a user, and that same session token at a later point might get picked up and created as a new session with the same id because it's deemed to be fair game to be used.