Restrict user login + AX 2012

Following Code in startupPost method of info class in AOT

void startupPost()
{
// To restrict user login form second login
xSession session;
SysClientSessions SysClientSessions;
UserId currentUserId;
int counter;

;

currentUserId = curUserId();

if(currentUserId!="Admin")// Allow Admin User to login multiple time
{
while select SysClientSessions
where SysClientSessions.userId == currentUserId &&
SysClientSessions.Status == 1 // 1 : Login 0 : Logout
{
session = new xSession(SysClientSessions.SessionId, true);
if (session && session.userId())
{
counter++;
}
}

if(counter>=2)
{
Box::stop("Already Logged-in : The same user id can't log in twice.");
infolog.shutDown(true);
}
}
}