diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -29,16 +29,26 @@
       return false
     end
 
-    #Configuration.reload
     # check if run in single user mode
-    if (Configuration[SINGLE_USER_MODE_CONF_KEY])
+    if Configuration[SINGLE_USER_MODE_CONF_KEY]
       user = User.find(session[:user_id])
       if user==nil or (not user.admin?)
         redirect_to :controller => 'main', :action => 'login'
         return false
       end
+      return true
     end
 
+    if Configuration.multicontests? 
+      user = User.find(session[:user_id])
+      begin
+        if user.contest_stat(true).forced_logout
+          flash[:notice] = 'You have been automatically logged out.'
+          redirect_to :controller => 'main', :action => 'index'
+        end
+      rescue
+      end
+    end
     return true
   end
 
diff --git a/app/controllers/login_controller.rb b/app/controllers/login_controller.rb
--- a/app/controllers/login_controller.rb
+++ b/app/controllers/login_controller.rb
@@ -10,6 +10,18 @@
     if user = User.authenticate(params[:login], params[:password])
       session[:user_id] = user.id
       session[:admin] = user.admin?
+
+      # clear forced logout flag for multicontests contest change
+      if Configuration.multicontests?
+        contest_stat = user.contest_stat
+        if contest_stat.respond_to? :forced_logout
+          if contest_stat.forced_logout
+            contest_stat.forced_logout = false
+            contest_stat.save
+          end
+        end
+      end
+
       redirect_to :controller => 'main', :action => 'list'
     else
       flash[:notice] = 'Wrong password'
diff --git a/app/controllers/main_controller.rb b/app/controllers/main_controller.rb
--- a/app/controllers/main_controller.rb
+++ b/app/controllers/main_controller.rb
@@ -343,6 +343,13 @@
     if not session[:user_id]
       render :text => 'Access forbidden', :status => 403
     end
+
+    if Configuration.multicontests?
+      user = User.find(session[:user_id])
+      if user.contest_stat.forced_logout
+        render :text => 'Access forbidden', :status => 403
+      end
+    end
   end
 
 end
diff --git a/app/controllers/user_admin_controller.rb b/app/controllers/user_admin_controller.rb
--- a/app/controllers/user_admin_controller.rb
+++ b/app/controllers/user_admin_controller.rb
@@ -196,7 +196,7 @@
     end
 
     note = []
-    user_ids = {}
+    users = []
     lines.split("\n").each do |line|
       user = User.find_by_login(line.chomp)
       if user
@@ -210,15 +210,18 @@
           user.contests = [contest]
         end
 
-        user.contest_stat.destroy if params[:reset_timer]
+        if params[:reset_timer]
+          user.contest_stat.forced_logout = true
+          user.contest_stat.reset_timer_and_save
+        end
 
         note << user.login
-        user_ids[user.id] = true
+        users << user
       end
     end
 
     if params[:reset_timer]
-      logout_users(user_ids)
+      logout_users(users)
     end
 
     flash[:notice] = 'User(s) ' + note.join(', ') + 
@@ -331,11 +334,12 @@
 
   end
 
-  def logout_users(user_ids)
-    sessions = ActiveRecord::SessionStore::Session.find(:all, :conditions => ["updated_at >= ?", 60.minutes.ago])
-    sessions.each do |session|
-      if user_ids.has_key? session.data[:user_id]
-        session.destroy
+  def logout_users(users)
+    users.each do |user|
+      contest_stat = user.contest_stat(true)
+      if contest_stat and !contest_stat.forced_logout
+        contest_stat.forced_logout = true
+        contest_stat.save
       end
     end
   end
diff --git a/app/models/user.rb b/app/models/user.rb
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -133,7 +133,7 @@
       if time_limit == nil
         return nil
       end
-      if contest_stat==nil
+      if contest_stat==nil or contest_stat.started_at==nil
         return (Time.now.gmtime + time_limit) - Time.now.gmtime
       else
         finish_time = contest_stat.started_at + time_limit
@@ -172,9 +172,9 @@
 
   def update_start_time
     stat = self.contest_stat
-    if stat == nil
-      stat = UserContestStat.new(:user => self,
-                                 :started_at => Time.now.gmtime)
+    if stat == nil or stat.started_at == nil
+      stat ||= UserContestStat.new(:user => self)
+      stat.started_at = Time.now.gmtime
       stat.save
     end
   end
diff --git a/app/models/user_contest_stat.rb b/app/models/user_contest_stat.rb
--- a/app/models/user_contest_stat.rb
+++ b/app/models/user_contest_stat.rb
@@ -2,4 +2,9 @@
 
   belongs_to :user
 
+  def reset_timer_and_save
+    self.started_at = nil
+    save
+  end
+
 end
diff --git a/db/migrate/20100328123325_add_forced_logout_to_user_contest_stat.rb b/db/migrate/20100328123325_add_forced_logout_to_user_contest_stat.rb
new file mode 100644
--- /dev/null
+++ b/db/migrate/20100328123325_add_forced_logout_to_user_contest_stat.rb
@@ -0,0 +1,9 @@
+class AddForcedLogoutToUserContestStat < ActiveRecord::Migration
+  def self.up
+    add_column :user_contest_stats, :forced_logout, :boolean
+  end
+
+  def self.down
+    remove_column :user_contest_stats, :forced_logout, :boolean
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -9,7 +9,7 @@
 #
 # It's strongly recommended to check this file into your version control system.
 
-ActiveRecord::Schema.define(:version => 20100303095700) do
+ActiveRecord::Schema.define(:version => 20100328123325) do
 
   create_table "announcements", :force => true do |t|
     t.string   "author"
@@ -210,6 +210,7 @@
     t.datetime "started_at"
     t.datetime "created_at"
     t.datetime "updated_at"
+    t.boolean  "forced_logout"
   end
 
   create_table "users", :force => true do |t|
diff --git a/public/javascripts/announcement_refresh.js b/public/javascripts/announcement_refresh.js
--- a/public/javascripts/announcement_refresh.js
+++ b/public/javascripts/announcement_refresh.js
@@ -20,16 +20,17 @@
 	    method: 'get',
 	    parameters: { recent: Announcement.mostRecentId },
 	    onSuccess: function(transport) {
-		if(transport.responseText.match(/\S/)!=null) {
+		if((transport.status == 200) && 
+		   (transport.responseText.match(/\S/)!=null)) {
  		    var announcementBody = $("announcementbox-body");
 		    announcementBody.insert({ top: transport.responseText });
 		    var announcementBoxes = $$(".announcementbox");
 		    if(announcementBoxes.length!=0)
 			announcementBoxes[0].show();
+		    Announcement.registerRefreshEventTimer();
 		}
 	    }
 	});
-	Announcement.registerRefreshEventTimer();
     },
 
     registerRefreshEventTimer: function() {
diff --git a/spec/controllers/user_admin_controller_spec.rb b/spec/controllers/user_admin_controller_spec.rb
new file mode 100644
--- /dev/null
+++ b/spec/controllers/user_admin_controller_spec.rb
@@ -0,0 +1,73 @@
+require 'delorean'
+
+require File.dirname(__FILE__) + '/../spec_helper'
+require File.dirname(__FILE__) + '/../config_spec_helper'
+
+describe UserAdminController, "when manage contest" do
+
+  include ConfigSpecHelperMethods
+
+  fixtures :users
+  fixtures :problems
+  fixtures :contests
+  fixtures :roles
+
+  def change_users_contest_to(user_login_list, contest, reset_timer=false)
+    post_data = {
+      :contest => {:id => contest.id},
+      :operation => 'assign',
+      :login_list => user_login_list
+    }
+    post_data[:reset_timer] = true if reset_timer
+    post 'manage_contest', post_data, {:user_id => @admin_user.id}
+  end
+
+  before(:each) do
+    @admin_user = users(:mary)
+    @contest_b = contests(:contest_b)
+    @james = users(:james)
+    @jack = users(:jack)
+
+    set_contest_time_limit('3:00')
+    set_indv_contest_mode
+  end
+
+  it "should allow admin to see contest management page" do
+    get 'contest_management', {}, {:user_id => @admin_user.id}
+
+    response.should render_template 'user_admin/contest_management'
+  end
+
+  it "should change users' contest" do
+    change_users_contest_to("james\njack", @contest_b)
+    response.should redirect_to :action => 'contest_management'
+
+    @james.contests(true).should include @contest_b
+    @jack.contests(true).should_not include @contest_a
+  end
+
+  it "should reset users' timer when their contests change" do
+    @james.update_start_time
+
+    Delorean.time_travel_to(190.minutes.since) do
+      @james.contest_finished?.should be_true
+
+      change_users_contest_to("james", @contest_b, true)
+
+      @james.contest_finished?.should be_false
+    end
+  end
+
+  it "should set forced_logout flag for users when their contests change" do
+    @james.update_start_time
+
+    Delorean.time_travel_to(190.minutes.since) do
+      @james.contest_finished?.should be_true
+
+      change_users_contest_to("james", @contest_b, true)
+
+      @james.contest_stat(true).forced_logout.should be_true
+    end
+  end
+
+end
diff --git a/spec/integration/contest_managements_spec.rb b/spec/integration/contest_managements_spec.rb
--- a/spec/integration/contest_managements_spec.rb
+++ b/spec/integration/contest_managements_spec.rb
@@ -18,6 +18,7 @@
 
     set_contest_time_limit('3:00')
     set_indv_contest_mode
+    enable_multicontest
   end
 
   it "should reset users' timer when their contests change" do
@@ -42,6 +43,30 @@
     end
   end
 
+  it "should force users to log out when their contests change" do
+    james_session = open_session
+    james_session.extend(MainSessionMethods)
+
+    james_login_and_get_main_list(james_session)
+    james_session.response.should_not have_text(/OVER/)
+
+    Delorean.time_travel_to(190.minutes.since) do
+      james_session.get_main_list
+      james_session.response.should have_text(/OVER/)
+
+      admin_change_users_contest_to("james", @contest_b, true)
+
+      james_session.get '/main/list'
+      james_session.response.should_not render_template 'main/list'
+      james_session.should be_redirect
+
+      Delorean.time_travel_to(200.minutes.since) do
+        james_login_and_get_main_list(james_session)
+        james_session.response.should_not have_text(/OVER/)
+      end
+    end
+  end
+
   private
 
   module MainSessionMethods
@@ -54,6 +79,11 @@
       get '/main/list'
       assert_template 'main/list'
     end
+
+    def get_main_list_and_assert_logout
+      get '/main/list'
+      assert_redirected_to '/main'
+    end
   end
 
   module ContestManagementSessionMethods