diff --git a/app/controllers/users/omniauth_callbacks_controller.rb b/app/controllers/users/omniauth_callbacks_controller.rb
index 0bdd2a801..81eaa08cb 100644
--- a/app/controllers/users/omniauth_callbacks_controller.rb
+++ b/app/controllers/users/omniauth_callbacks_controller.rb
@@ -41,9 +41,7 @@ class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
     end
 
     def save_user(user)
-      @user.save ||
-      @user.save_requiring_finish_signup ||
-      @user.save_requiring_finish_signup_without_email
+      @user.save || @user.save_requiring_finish_signup
     end
 
 end
diff --git a/app/models/user.rb b/app/models/user.rb
index f7980c796..ea889ac57 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -26,7 +26,7 @@ class User < ActiveRecord::Base
   belongs_to :geozone
 
   validates :username, presence: true, if: :username_required?
-  validates :username, uniqueness: true, if: :username_required?
+  validates :username, uniqueness: { scope: :registering_with_oauth }, if: :username_required?
   validates :document_number, uniqueness: { scope: :document_type }, allow_nil: true
 
   validate :validate_username_length
@@ -154,6 +154,7 @@ class User < ActiveRecord::Base
       confirmed_phone: nil,
       unconfirmed_phone: nil
     )
+    self.identities.destroy_all
   end
 
   def erased?
@@ -182,11 +183,11 @@ class User < ActiveRecord::Base
   end
 
   def username_required?
-    !organization? && !erased? && !registering_with_oauth
+    !organization? && !erased?
   end
 
   def email_required?
-    !erased? && !registering_with_oauth
+    !erased?
   end
 
   def has_official_email?
@@ -215,11 +216,15 @@ class User < ActiveRecord::Base
   end
 
   def save_requiring_finish_signup
-    self.update(registering_with_oauth: true)
-  end
-
-  def save_requiring_finish_signup_without_email
-    self.update(registering_with_oauth: true, email: nil)
+    begin
+      self.registering_with_oauth = true
+      self.save(validate: false)
+    # Devise puts unique constraints for the email the db, so we must detect & handle that
+    rescue ActiveRecord::RecordNotUnique
+      self.email = nil
+      self.save(validate: false)
+    end
+    true
   end
 
   def ability
diff --git a/app/views/users/registrations/finish_signup.html.erb b/app/views/users/registrations/finish_signup.html.erb
index fa7bb621e..79f160a51 100644
--- a/app/views/users/registrations/finish_signup.html.erb
+++ b/app/views/users/registrations/finish_signup.html.erb
@@ -3,6 +3,10 @@
 <%= form_for current_user, as: :user, url: do_finish_signup_path, html: { role: 'form'} do |f| %>
   <%= render 'shared/errors', resource: current_user %>
 
+  <div class='callout primary'>
+    <%= t("omniauth.finish_signup.username_warning") %>
+  </div>
+
   <% if current_user.errors.include? :username %>
     <%= f.text_field :username, placeholder: t("devise_views.users.registrations.new.username_label") %>
   <% else %>
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 8609c079c..b5899e63a 100755
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -542,6 +542,7 @@ en:
   omniauth:
     finish_signup:
       title: "Additional details"
+      username_warning: "Due to a change in the way we interact with social networks, it is possible that your username now appears as 'already in use'. If that is your case, please choose a different username."
     twitter:
       sign_in: "Sign in with Twitter"
       sign_up: "Sign up with Twitter"
diff --git a/config/locales/es.yml b/config/locales/es.yml
index a15528d5a..f1241bb15 100755
--- a/config/locales/es.yml
+++ b/config/locales/es.yml
@@ -542,6 +542,7 @@ es:
   omniauth:
     finish_signup:
       title: "Detalles adicionales de tu cuenta"
+      username_warning: "Debido a que hemos cambiado la forma en la que nos conectamos con redes sociales y es posible que tu nombre de usuario aparezca como 'ya en uso', incluso si antes podías acceder con él. Si es tu caso, por favor elige un nombre de usuario distinto."
     twitter:
       sign_in: "Entra con Twitter"
       sign_up: "Regístrate con Twitter"
diff --git a/db/migrate/20160418144013_add_index_to_username.rb b/db/migrate/20160418144013_add_index_to_username.rb
new file mode 100644
index 000000000..191f24ac6
--- /dev/null
+++ b/db/migrate/20160418144013_add_index_to_username.rb
@@ -0,0 +1,5 @@
+class AddIndexToUsername < ActiveRecord::Migration
+  def change
+    add_index :users, :username
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 223a14d47..49f0011f2 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -432,6 +432,7 @@ ActiveRecord::Schema.define(version: 20160418172919) do
   add_index "users", ["geozone_id"], name: "index_users_on_geozone_id", using: :btree
   add_index "users", ["hidden_at"], name: "index_users_on_hidden_at", using: :btree
   add_index "users", ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true, using: :btree
+  add_index "users", ["username"], name: "index_users_on_username", using: :btree
 
   create_table "valuation_assignments", force: :cascade do |t|
     t.integer  "valuator_id"
diff --git a/lib/tasks/users.rake b/lib/tasks/users.rake
index c56df2dd0..efbeeaa94 100644
--- a/lib/tasks/users.rake
+++ b/lib/tasks/users.rake
@@ -59,4 +59,21 @@ namespace :users do
     end
   end
 
+  desc "Makes duplicate username users change their username"
+  task social_network_reset: :environment do
+    duplicated_usernames = User.all.select(:username).group(:username).having('count(username) > 1').pluck(:username)
+
+    duplicated_usernames.each do |username|
+      print "."
+      user_ids = User.where(username: username).order(created_at: :asc).pluck(:id)
+      user_ids_to_review = Identity.where(user_id: user_ids).pluck(:user_id)
+      user_ids_to_review.shift if user_ids.size == user_ids_to_review.size
+      user_ids_to_review.each { |id| User.find(id).update(registering_with_oauth: true) }
+    end
+  end
+
+  desc "Removes identities associated to erased users"
+  task remove_erased_identities: :environment do
+    Identity.joins(:user).where('users.erased_at IS NOT NULL').destroy_all
+  end
 end
diff --git a/spec/features/users_auth_spec.rb b/spec/features/users_auth_spec.rb
index a1c9374be..f9b92bb12 100644
--- a/spec/features/users_auth_spec.rb
+++ b/spec/features/users_auth_spec.rb
@@ -169,6 +169,12 @@ feature 'Users' do
 
         expect(current_path).to eq(finish_signup_path)
 
+        expect(page).to have_field('user_username', with: 'manuela')
+
+        click_button 'Register'
+
+        expect(current_path).to eq(do_finish_signup_path)
+
         fill_in 'user_username', with: 'manuela2'
         click_button 'Register'
 
diff --git a/spec/models/user_spec.rb b/spec/models/user_spec.rb
index 4d1b269ec..b49e3cc6b 100644
--- a/spec/models/user_spec.rb
+++ b/spec/models/user_spec.rb
@@ -333,6 +333,7 @@ describe User do
                      email_verification_token: "token3",
                      confirmed_phone:"5678",
                      unconfirmed_phone:"5678")
+
       user.erase('a test')
       user.reload
 
@@ -353,6 +354,14 @@ describe User do
       expect(user.confirmation_token).to be_nil
       expect(user.reset_password_token).to be_nil
       expect(user.email_verification_token).to be_nil
+
+    end
+
+    it "destroys associated identities" do
+      user = create(:user)
+      identity = create(:identity, user: user)
+      user.erase('an identity test')
+      expect(Identity.exists?(identity.id)).to_not be
     end
   end