diff --git a/src/Umbraco.Core/TypeFinder.cs b/src/Umbraco.Core/TypeFinder.cs
index 6b7627e257..2630133a62 100644
--- a/src/Umbraco.Core/TypeFinder.cs
+++ b/src/Umbraco.Core/TypeFinder.cs
@@ -2,23 +2,18 @@
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
-using System.Diagnostics;
 using System.IO;
 using System.Linq;
-using System.Linq.Expressions;
 using System.Reflection;
 using System.Security;
 using System.Text;
 using System.Threading;
 using System.Web;
 using System.Web.Compilation;
-using System.Web.Hosting;
-using Umbraco.Core.Configuration;
 using Umbraco.Core.IO;
 
 namespace Umbraco.Core
 {
-
 	//TODO: Get the App_Code stuff in here from the old one
 
 	/// <summary>
@@ -27,7 +22,6 @@ namespace Umbraco.Core
 	/// </summary>
 	public static class TypeFinder
 	{
-		
 		private static readonly ConcurrentBag<Assembly> LocalFilteredAssemblyCache = new ConcurrentBag<Assembly>();
 		private static readonly ReaderWriterLockSlim LocalFilteredAssemblyCacheLocker = new ReaderWriterLockSlim();
 		private static ReadOnlyCollection<Assembly> _allAssemblies = null;
@@ -86,8 +80,7 @@ namespace Umbraco.Core
 						}
 
 						//now set the _allAssemblies
-						_allAssemblies = new ReadOnlyCollection<Assembly>(assemblies);						
-
+						_allAssemblies = new ReadOnlyCollection<Assembly>(assemblies);
 					}
 					catch (InvalidOperationException e)
 					{
@@ -100,8 +93,8 @@ namespace Umbraco.Core
 			}
 
 			return _allAssemblies;
-		}		
-		
+		}
+
 		/// <summary>
 		/// Returns only assemblies found in the bin folder that have been loaded into the app domain.
 		/// </summary>
@@ -111,7 +104,6 @@ namespace Umbraco.Core
 		/// </remarks>
 		internal static IEnumerable<Assembly> GetBinAssemblies()
 		{
-
 			if (_binFolderAssemblies == null)
 			{
 				using (new WriteLock(Locker))
@@ -143,7 +135,8 @@ namespace Umbraco.Core
 					{
 						try
 						{
-							var foundAssembly = safeDomainAssemblies.FirstOrDefault(a => a.GetAssemblyFile() == assemblyName.GetAssemblyFile());
+							var foundAssembly =
+								safeDomainAssemblies.FirstOrDefault(a => a.GetAssemblyFile() == assemblyName.GetAssemblyFile());
 							if (foundAssembly != null)
 							{
 								binFolderAssemblies.Add(foundAssembly);
@@ -162,7 +155,7 @@ namespace Umbraco.Core
 				}
 			}
 			return _binFolderAssemblies;
-		} 
+		}
 
 		/// <summary>
 		/// Return a list of found local Assemblies excluding the known assemblies we don't want to scan 
@@ -181,7 +174,7 @@ namespace Umbraco.Core
 				assemblies.ForEach(LocalFilteredAssemblyCache.Add);
 			}
 			return LocalFilteredAssemblyCache;
-		}		
+		}
 
 		/// <summary>
 		/// Return a list of found local Assemblies and exluding the ones passed in and excluding the exclusion list filter
@@ -190,18 +183,18 @@ namespace Umbraco.Core
 		/// <param name="exclusionFilter"></param>
 		/// <returns></returns>
 		private static IEnumerable<Assembly> GetFilteredAssemblies(
-			IEnumerable<Assembly> excludeFromResults = null, 
+			IEnumerable<Assembly> excludeFromResults = null,
 			string[] exclusionFilter = null)
 		{
 			if (excludeFromResults == null)
 				excludeFromResults = new List<Assembly>();
 			if (exclusionFilter == null)
-				exclusionFilter = new string[] { };
+				exclusionFilter = new string[] {};
 
 			return GetAllAssemblies()
 				.Where(x => !excludeFromResults.Contains(x)
-							&& !x.GlobalAssemblyCache
-							&& !exclusionFilter.Any(f => x.FullName.StartsWith(f)));
+				            && !x.GlobalAssemblyCache
+				            && !exclusionFilter.Any(f => x.FullName.StartsWith(f)));
 		}
 
 		/// <summary>
@@ -211,42 +204,42 @@ namespace Umbraco.Core
 		/// NOTE the comma vs period... comma delimits the name in an Assembly FullName property so if it ends with comma then its an exact name match
 		/// </remarks>
 		internal static readonly string[] KnownAssemblyExclusionFilter = new[]
-                {
-                    "mscorlib,",
-					"System.",
-                    "Antlr3.",
-                    "Autofac.",
-                    "Autofac,",
-                    "Castle.",
-                    "ClientDependency.",
-                    "DataAnnotationsExtensions.",
-                    "DataAnnotationsExtensions,",
-                    "Dynamic,",
-                    "HtmlDiff,",
-                    "Iesi.Collections,",
-                    "log4net,",
-                    "Microsoft.",
-                    "Newtonsoft.",
-                    "NHibernate.",
-                    "NHibernate,",
-                    "NuGet.",
-                    "RouteDebugger,",
-                    "SqlCE4Umbraco,",
-                    "umbraco.datalayer,",
-                    "umbraco.interfaces,",										
-					"umbraco.providers,",
-					"Umbraco.Web.UI,",
-					"umbraco.webservices",
-                    "Lucene.",
-                    "Examine,",
-                    "Examine.",
-                    "ServiceStack.",
-                    "MySql.",
-                    "HtmlAgilityPack.",
-                    "TidyNet.",
-                    "ICSharpCode.",
-                    "CookComputing."
-                };
+			{
+				"mscorlib,",
+				"System.",
+				"Antlr3.",
+				"Autofac.",
+				"Autofac,",
+				"Castle.",
+				"ClientDependency.",
+				"DataAnnotationsExtensions.",
+				"DataAnnotationsExtensions,",
+				"Dynamic,",
+				"HtmlDiff,",
+				"Iesi.Collections,",
+				"log4net,",
+				"Microsoft.",
+				"Newtonsoft.",
+				"NHibernate.",
+				"NHibernate,",
+				"NuGet.",
+				"RouteDebugger,",
+				"SqlCE4Umbraco,",
+				"umbraco.datalayer,",
+				"umbraco.interfaces,",
+				"umbraco.providers,",
+				"Umbraco.Web.UI,",
+				"umbraco.webservices",
+				"Lucene.",
+				"Examine,",
+				"Examine.",
+				"ServiceStack.",
+				"MySql.",
+				"HtmlAgilityPack.",
+				"TidyNet.",
+				"ICSharpCode.",
+				"CookComputing."
+			};
 
 		public static IEnumerable<Type> FindClassesOfTypeWithAttribute<T, TAttribute>()
 			where TAttribute : Attribute
@@ -260,13 +253,19 @@ namespace Umbraco.Core
 			return FindClassesOfTypeWithAttribute<T, TAttribute>(assemblies, true);
 		}
 
-		public static IEnumerable<Type> FindClassesOfTypeWithAttribute<T, TAttribute>(IEnumerable<Assembly> assemblies, bool onlyConcreteClasses)
+		public static IEnumerable<Type> FindClassesOfTypeWithAttribute<T, TAttribute>(IEnumerable<Assembly> assemblies,
+		                                                                              bool onlyConcreteClasses)
 			where TAttribute : Attribute
 		{
 			if (assemblies == null) throw new ArgumentNullException("assemblies");
 
+			// a assembly cant contain types that are assignable to a type it doesn't reference
+			assemblies = RemoveAssembliesThatDontReferenceAssemblyOfType(typeof (T), assemblies);
+			// a assembly cant contain types with a attribute it doesn't reference
+			assemblies = RemoveAssembliesThatDontReferenceAssemblyOfType(typeof (TAttribute), assemblies);
+
 			var l = new List<Type>();
-			foreach(var a in assemblies)
+			foreach (var a in assemblies)
 			{
 				var types = from t in GetTypesWithFormattedException(a)
 				            where !t.IsInterface
@@ -325,7 +324,7 @@ namespace Umbraco.Core
 		public static IEnumerable<Type> FindClassesWithAttribute<T>(IEnumerable<Assembly> assemblies, bool onlyConcreteClasses)
 			where T : Attribute
 		{
-			return FindClassesWithAttribute(typeof(T), assemblies, onlyConcreteClasses);
+			return FindClassesWithAttribute(typeof (T), assemblies, onlyConcreteClasses);
 		}
 
 		/// <summary>
@@ -335,23 +334,58 @@ namespace Umbraco.Core
 		/// <param name="assemblies">The assemblies.</param>
 		/// <param name="onlyConcreteClasses">if set to <c>true</c> only concrete classes.</param>
 		/// <returns></returns>
-		public static IEnumerable<Type> FindClassesWithAttribute(Type type, IEnumerable<Assembly> assemblies, bool onlyConcreteClasses)
+		public static IEnumerable<Type> FindClassesWithAttribute(Type type, IEnumerable<Assembly> assemblies,
+		                                                         bool onlyConcreteClasses)
 		{
 			if (assemblies == null) throw new ArgumentNullException("assemblies");
 			if (!TypeHelper.IsTypeAssignableFrom<Attribute>(type))
 				throw new ArgumentException("The type specified: " + type + " is not an Attribute type");
+			// a assembly cant contain types with a attribute it doesn't reference
+			assemblies = RemoveAssembliesThatDontReferenceAssemblyOfType(type, assemblies);
 
 			var l = new List<Type>();
 			foreach (var a in assemblies)
 			{
 				var types = from t in GetTypesWithFormattedException(a)
-							where !t.IsInterface && t.GetCustomAttributes(type, false).Any() && (!onlyConcreteClasses || (t.IsClass && !t.IsAbstract))
-							select t;
+				            where
+					            !t.IsInterface && t.GetCustomAttributes(type, false).Any() &&
+					            (!onlyConcreteClasses || (t.IsClass && !t.IsAbstract))
+				            select t;
 				l.AddRange(types);
 			}
 
 			return l;
 		}
+		/// <summary>
+		/// Removes assemblies that doesn't reference the assembly of the type we are looking for.
+		/// </summary>
+		/// <param name="type"></param>
+		/// <param name="assemblies"></param>
+		/// <returns></returns>
+		private static IEnumerable<Assembly> RemoveAssembliesThatDontReferenceAssemblyOfType(Type type,
+		                                                                                     IEnumerable<Assembly> assemblies)
+		{
+			// Avoid scanning assembly if it doesn't contain a reference to the assembly containing the type we are looking for 
+			// to the assembly containing the attribute we are looking for
+			var assemblyNameOfType = type.Assembly.GetName().Name;
+
+			return assemblies
+				.Where(assembly => assembly == type.Assembly
+				                   || HasReferenceToAssemblyWithName(assembly, assemblyNameOfType)).ToList();
+		}
+		/// <summary>
+		/// checks if the assembly has a reference with the same name as the expected assembly name.
+		/// </summary>
+		/// <param name="assembly"></param>
+		/// <param name="expectedAssemblyName"></param>
+		/// <returns></returns>
+		private static bool HasReferenceToAssemblyWithName(Assembly assembly, string expectedAssemblyName)
+		{
+			return assembly
+				.GetReferencedAssemblies()
+				.Select(a => a.Name)
+				.Contains(expectedAssemblyName, StringComparer.Ordinal);
+		}
 
 		/// <summary>
 		/// Finds the classes with attribute.
@@ -376,9 +410,8 @@ namespace Umbraco.Core
 			return FindClassesWithAttribute<T>(GetAssembliesWithKnownExclusions());
 		}
 
-
 		#region Private methods
-		
+
 		/// <summary>
 		/// Gets a collection of assignables of type T from a collection of assemblies
 		/// </summary>
@@ -388,20 +421,26 @@ namespace Umbraco.Core
 		/// <returns></returns>
 		private static IEnumerable<Type> GetAssignablesFromType<T>(IEnumerable<Assembly> assemblies, bool onlyConcreteClasses)
 		{
-			return GetTypes(typeof(T), assemblies, onlyConcreteClasses);
+			return GetTypes(typeof (T), assemblies, onlyConcreteClasses);
 		}
 
-		private static IEnumerable<Type> GetTypes(Type assignTypeFrom, IEnumerable<Assembly> assemblies, bool onlyConcreteClasses)
+		private static IEnumerable<Type> GetTypes(Type assignTypeFrom, IEnumerable<Assembly> assemblies,
+		                                          bool onlyConcreteClasses)
 		{
+			// a assembly cant contain types that are assignable to a type it doesn't reference
+			assemblies = RemoveAssembliesThatDontReferenceAssemblyOfType(assignTypeFrom, assemblies);
+
 			var l = new List<Type>();
 			foreach (var a in assemblies)
 			{
 				var types = from t in GetTypesWithFormattedException(a)
-				            where !t.IsInterface && assignTypeFrom.IsAssignableFrom(t) && (!onlyConcreteClasses || (t.IsClass && !t.IsAbstract))
+				            where
+					            !t.IsInterface && assignTypeFrom.IsAssignableFrom(t) &&
+					            (!onlyConcreteClasses || (t.IsClass && !t.IsAbstract))
 				            select t;
 				l.AddRange(types);
 			}
-			return l;			
+			return l;
 		}
 
 		private static IEnumerable<Type> GetTypesWithFormattedException(Assembly a)
@@ -420,15 +459,12 @@ namespace Umbraco.Core
 				sb.AppendLine("Could not load types from assembly " + a.FullName + ", errors:");
 				foreach (var loaderException in ex.LoaderExceptions.WhereNotNull())
 				{
-					sb.AppendLine("Exception: " + loaderException.ToString());
+					sb.AppendLine("Exception: " + loaderException);
 				}
 				throw new ReflectionTypeLoadException(ex.Types, ex.LoaderExceptions, sb.ToString());
 			}
 		}
 
 		#endregion
-
-
-		
 	}
-}
+}
\ No newline at end of file