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Posted 12 Jul 2011

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Prevent Simultaneous Logins by a Single User ID in ASP.NET

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12 Jul 2011CPOL
Using this code block, you can prevent simultaneous logins by a single User ID.

Using this code block, you can prevent simultaneous logins by a single User ID.

In order to use this code, you need to have your customized session based authentication method, which means that in your login method, you need to fetch the user from your storage (database, XML ...) and create a user object and put it in the Session. After that, the following code block should be used:

Hashtable sessions = (Hashtable)Application["WEB_SESSIONS_OBJECT"];
//"sessionsthis will be a pointer to all

Your login method will look like this:

void yourLoginMethod(string userID, string password)
    //put your login logic here and put the logged in user object in the session.

    //getting the sessions objects from the Application
    Hashtable sessions = (Hashtable)Application["WEB_SESSIONS_OBJECT"];
    if (sessions == null)
        sessions = new Hashtable();

    //getting the pointer to the Session of the current logged in user
    HttpSessionState existingUserSession = 
         (HttpSessionState)sessions[userID]; if (existingUserSession != null)
        existingUserSession[WebKeys.USEROBJECT] = null;
        //logout current logged in user

    //putting the user in the session
    Session[WebKeys.USEROBJECT] = user;
    sessions[user.UserName] = Session;
    Application.Lock(); //lock to prevent duplicate objects
    Application["WEB_SESSIONS_OBJECT"] = sessions;

Your logout method will look like this:

void yourLogoutMethod(string userID)
    //put your logout logic here, remove the user object from the session.
    Hashtable sessions = (Hashtable)Application["WEB_SESSIONS_OBJECT"];
    if (sessions == null)
        sessions = new Hashtable();


    Application["WEB_SESSIONS_OBJECT"] = sessions;


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Bahram Ettehadieh
Web Developer
Iran (Islamic Republic of) Iran (Islamic Republic of)
I hold a BS degree in software engineering and am a Microsoft Certified Solution Developer(MCSD).
I have more than 8 years of experience in .NET developement, mostly web develop using C# and ASP.NET.

Comments and Discussions

QuestionWebKeys.USEROBJECT Pin
Prasad Nagabathula16-Jul-12 1:45
MemberPrasad Nagabathula16-Jul-12 1:45 
Generalwebsites like yahoo, gmail... sign out the first user when t... Pin
Bahram Ettehadieh28-Nov-11 20:58
MemberBahram Ettehadieh28-Nov-11 20:58 
GeneralRe: websites like yahoo, gmail... sign out the first user when t... Pin
tara_sh50021-Sep-15 15:27
Membertara_sh50021-Sep-15 15:27 
I'm still not sure what is WebKeys here? should we declare it before as object?
also user.UserName which is used in session , is it an object(user)?
please clarify the code, or attach a code sample .


GeneralWhat happends when someone not clicking on signout buttton. ... Pin
Seetaram Yadav29-Jul-11 2:58
MemberSeetaram Yadav29-Jul-11 2:58 
GeneralWe did something similar at my last company to prevent shari... Pin
Matthew A Jones21-Jul-11 3:52
MemberMatthew A Jones21-Jul-11 3:52 
GeneralRe: I did something similar for our company's web app, any login... Pin
daleofcourse12-Oct-11 6:19
Memberdaleofcourse12-Oct-11 6:19 
GeneralThis method doesn't prevent multiple windows in the same bro... Pin
AndyHo18-Jul-11 13:17
professionalAndyHo18-Jul-11 13:17 
GeneralRe: I'm not sure that's possible, at least using server side cod... Pin
Bahram Ettehadieh19-Jul-11 19:36
MemberBahram Ettehadieh19-Jul-11 19:36 

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