diff --git a/models/user/user.go b/models/user/user.go
index 5709ed7ff2..5f152780bf 100644
--- a/models/user/user.go
+++ b/models/user/user.go
@@ -41,6 +41,18 @@ const (
 
 	// UserTypeOrganization defines an organization
 	UserTypeOrganization
+
+	// UserTypeReserved reserves a (non-existing) user, i.e. to prevent a spam user from re-registering after being deleted, or to reserve the name until the user is actually created later on
+	UserTypeUserReserved
+
+	// UserTypeOrganizationReserved reserves a (non-existing) organization, to be used in combination with UserTypeUserReserved
+	UserTypeOrganizationReserved
+
+	// UserTypeBot defines a bot user
+	UserTypeBot
+
+	// UserTypeRemoteUser defines a remote user for federated users
+	UserTypeRemoteUser
 )
 
 const (
@@ -312,6 +324,7 @@ func GetUserFollowers(ctx context.Context, u, viewer *User, listOptions db.ListO
 		Select("`user`.*").
 		Join("LEFT", "follow", "`user`.id=follow.user_id").
 		Where("follow.follow_id=?", u.ID).
+		And("`user`.type=?", UserTypeIndividual).
 		And(isUserVisibleToViewerCond(viewer))
 
 	if listOptions.Page != 0 {
@@ -333,6 +346,7 @@ func GetUserFollowing(ctx context.Context, u, viewer *User, listOptions db.ListO
 		Select("`user`.*").
 		Join("LEFT", "follow", "`user`.id=follow.follow_id").
 		Where("follow.user_id=?", u.ID).
+		And("`user`.type=?", UserTypeIndividual).
 		And(isUserVisibleToViewerCond(viewer))
 
 	if listOptions.Page != 0 {
@@ -959,7 +973,7 @@ func GetUserByName(ctx context.Context, name string) (*User, error) {
 	if len(name) == 0 {
 		return nil, ErrUserNotExist{0, name, 0}
 	}
-	u := &User{LowerName: strings.ToLower(name)}
+	u := &User{LowerName: strings.ToLower(name), Type: UserTypeIndividual}
 	has, err := db.GetEngine(ctx).Get(u)
 	if err != nil {
 		return nil, err
diff --git a/services/auth/source/db/authenticate.go b/services/auth/source/db/authenticate.go
index ec89984499..76445e0d6d 100644
--- a/services/auth/source/db/authenticate.go
+++ b/services/auth/source/db/authenticate.go
@@ -40,5 +40,13 @@ func Authenticate(user *user_model.User, login, password string) (*user_model.Us
 		}
 	}
 
+	// attempting to login as a non-user account
+	if user.Type != user_model.UserTypeIndividual {
+		return nil, user_model.ErrUserProhibitLogin{
+			UID:  user.ID,
+			Name: user.Name,
+		}
+	}
+
 	return user, nil
 }