diff --git a/hooks/conan-center.py b/hooks/conan-center.py
index b0b7b52f..ed3df651 100644
--- a/hooks/conan-center.py
+++ b/hooks/conan-center.py
@@ -7,13 +7,15 @@
 import sys
 from logging import WARNING, ERROR, INFO, DEBUG, NOTSET
 
+from conans import tools, ConanFile
+
 import yaml
-from conans import tools
 try:
     from conans import Settings
 except ImportError:
     from conans.model.settings import Settings
 
+
 kb_errors = {"KB-H001": "DEPRECATED GLOBAL CPPSTD",
              "KB-H002": "REFERENCE LOWERCASE",
              "KB-H003": "RECIPE METADATA",
@@ -46,6 +48,7 @@
              "KB-H031": "CONANDATA.YML REDUCE",
              "KB-H032": "SYSTEM REQUIREMENTS",
              "KB-H034": "TEST PACKAGE - NO IMPORTS()",
+             "KB-H035": "CUSTOM ATTRIBUTES",
              "KB-H037": "NO AUTHOR",
              "KB-H040": "NO TARGET NAME",
              "KB-H041": "NO FINAL ENDLINE",
@@ -421,6 +424,19 @@ def test(out):
         if "def imports" in test_package_conanfile:
             out.error("The method `imports` is not allowed in test_package/conanfile.py")
 
+    @run_test("KB-H035", output)
+    def test(out):
+        mock = ConanFile(conanfile.output, None)
+        valid_attrs = [attr for attr in dir(mock) if not callable(attr)] + ['conan_data', 'python_requires']
+        current_attrs = [attr for attr in dir(conanfile) if not callable(attr)]
+        invalid_attrs = re.findall(r"(__.*)\s?=", conanfile_content, re.MULTILINE)
+        for attr in current_attrs:
+            if not attr.startswith("_") and attr not in valid_attrs:
+                invalid_attrs.append(attr)
+        if invalid_attrs:
+            out.error("Custom attributes must be declared as protected. " \
+                      "The follow attributes are invalid: '{}'".format("', '".join(invalid_attrs)))
+
     @run_test("KB-H037", output)
     def test(out):
         author = getattr(conanfile, "author", None)
diff --git a/tests/test_hooks/conan-center/test_conan-center.py b/tests/test_hooks/conan-center/test_conan-center.py
index 8f8e7cc2..fc48d136 100644
--- a/tests/test_hooks/conan-center/test_conan-center.py
+++ b/tests/test_hooks/conan-center/test_conan-center.py
@@ -118,6 +118,7 @@ def test_conanfile(self):
         self.assertIn("ERROR: [CONAN CENTER INDEX URL (KB-H027)] The attribute 'url' should " \
                       "point to: https://github.com/conan-io/conan-center-index", output)
         self.assertIn("[CMAKE MINIMUM VERSION (KB-H028)] OK", output)
+        self.assertIn("[CUSTOM ATTRIBUTES (KB-H035)] OK", output)
         self.assertIn("[SYSTEM REQUIREMENTS (KB-H032)] OK", output)
         self.assertIn("[SINGLE REQUIRES (KB-H055)] OK", output)
 
@@ -141,6 +142,7 @@ def test_conanfile_header_only(self):
                       "recipe", output)
         self.assertIn("[META LINES (KB-H025)] OK", output)
         self.assertIn("[CMAKE MINIMUM VERSION (KB-H028)] OK", output)
+        self.assertIn("[CUSTOM ATTRIBUTES (KB-H035)] OK", output)
         self.assertIn("[SYSTEM REQUIREMENTS (KB-H032)] OK", output)
 
     def test_conanfile_header_only_with_settings(self):
@@ -162,6 +164,7 @@ def test_conanfile_header_only_with_settings(self):
                       "recipe", output)
         self.assertIn("[META LINES (KB-H025)] OK", output)
         self.assertIn("[CMAKE MINIMUM VERSION (KB-H028)] OK", output)
+        self.assertIn("[CUSTOM ATTRIBUTES (KB-H035)] OK", output)
         self.assertIn("[SYSTEM REQUIREMENTS (KB-H032)] OK", output)
 
     def test_conanfile_settings_clear_with_settings(self):
@@ -604,6 +607,42 @@ def system_requirements(self):
         self.assertIn("[SYSTEM REQUIREMENTS (KB-H032)] 'libusb' is part of the allowlist.", output)
         self.assertNotIn("ERROR: [SYSTEM REQUIREMENTS (KB-H032)]", output)
 
+    def test_invalid_recipe_attributes(self):
+        conanfile = textwrap.dedent("""\
+        from conans import ConanFile
+
+        class AConan(ConanFile):
+            url = "fake_url.com"
+            license = "fake_license"
+            description = "whatever"
+            homepage = "homepage.com"
+            topics = ("fake_topic", "another_fake_topic")
+            exports_sources = "header.h"
+            options = {"foo": [True, False], "bar": [True, False]}
+            default_options = {"foo": False, "bar": True}
+            _source_subfolder = "source_subfolder"
+            _build_subfolder = "build_subfolder"
+            __my_private = "secret"
+            __attribute__ = "foobar"
+            __qux= "baz"
+            foobar = "package"
+            package_subfolder = "package"
+
+            def package(self):
+                self.copy("*", dst="include")
+
+            def _foobar(self):
+                pass
+
+            def __private(self):
+                pass
+        """)
+        tools.save('conanfile.py', content=conanfile)
+        output = self.conan(['create', '.', 'name/version@user/test'])
+        self.assertIn("ERROR: [CUSTOM ATTRIBUTES (KB-H035)] Custom attributes must be declared as "
+                      "protected. The follow attributes are invalid: '__my_private ', "
+                      "'__attribute__ ', '__qux', 'foobar', 'package_subfolder'", output)
+
     def test_imports_not_allowed(self):
         conanfile_tp = textwrap.dedent("""\
         from conans import ConanFile, tools