diff --git a/OpenRA.FileFormats/Verifier.cs b/OpenRA.FileFormats/Verifier.cs
index 532e4d95ed..0300bad1d6 100644
--- a/OpenRA.FileFormats/Verifier.cs
+++ b/OpenRA.FileFormats/Verifier.cs
@@ -18,13 +18,169 @@
  */
 #endregion
 
+using System;
+using System.Reflection;
+using System.Collections.Generic;
+using System.Reflection.Emit;
+using System.Linq;
+
 namespace OpenRA.FileFormats
 {
 	public static class Verifier
 	{
-		public static bool IsSafe(string filename)
+		static readonly string[] AllowedPatterns = {
+													   /* todo */
+												   };
+
+		public static bool IsSafe(string filename, List<string> failures)
 		{
-			return false;	// todo
+			AppDomain.CurrentDomain.ReflectionOnlyAssemblyResolve += (s, a) => Assembly.ReflectionOnlyLoad(a.Name);
+			var flags = BindingFlags.Instance | BindingFlags.Static |
+				BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.DeclaredOnly;
+
+			var assembly = Assembly.ReflectionOnlyLoadFrom(filename);
+
+			var pinvokes = assembly.GetTypes()
+				.SelectMany(t => t.GetMethods(flags))
+				.Where(m => (m.Attributes & MethodAttributes.PinvokeImpl) != 0)
+				.Select(m => m.Name).ToArray();
+
+			foreach (var pi in pinvokes)
+				failures.Add("P/Invoke: {0}".F(pi));
+
+			foreach (var fn in assembly
+				.GetTypes()
+				.SelectMany(x => x.GetMembers(flags))
+				.SelectMany(x => FunctionsUsedBy(x))
+				.Where(x => x.DeclaringType.Assembly != assembly)
+				.Select(x => string.Format("{0}:{1}", x.DeclaringType.FullName, x))
+				.OrderBy(x => x)
+				.Distinct())
+				if (!IsAllowed(fn))
+					failures.Add("Unsafe function: {0}".F(fn));
+
+			return failures.Count > 0;
+		}
+
+		static bool IsAllowed(string fn)
+		{
+			foreach (var p in AllowedPatterns)
+				if (p.EndsWith("*"))
+				{
+					if (fn.StartsWith(p.Substring(0, p.Length - 1))) return true;
+				}
+				else
+				{
+					if (fn == p) return true;
+				}
+
+			return false;
+		}
+
+		static IEnumerable<MethodBase> FunctionsUsedBy( MemberInfo x )
+		{
+			if( x is MethodInfo )
+			{
+				var method = x as MethodInfo;
+				if (method.GetMethodBody() != null)
+					foreach( var fn in CheckIL( method.GetMethodBody().GetILAsByteArray(), x.Module, x.DeclaringType.GetGenericArguments(), method.GetGenericArguments() ) )
+						yield return fn;
+			}
+			else if( x is ConstructorInfo )
+			{
+				var method = x as ConstructorInfo;
+				if (method.GetMethodBody() != null)
+					foreach( var fn in CheckIL( method.GetMethodBody().GetILAsByteArray(), x.Module, x.DeclaringType.GetGenericArguments(), new Type[ 0 ] ) )
+						yield return fn;
+			}
+			else if( x is FieldInfo )
+			{
+				// ignore it
+			}
+			else if( x is PropertyInfo )
+			{
+				var prop = x as PropertyInfo;
+				foreach( var method in prop.GetAccessors() )
+					if (method.GetMethodBody() != null)
+						foreach( var fn in CheckIL( method.GetMethodBody().GetILAsByteArray(), x.Module, x.DeclaringType.GetGenericArguments(), new Type[ 0 ] ) )
+							yield return fn;
+			}
+			else if( x is Type )
+			{
+				// ... shouldn't happen, but does.... :O
+			}
+			else
+				throw new NotImplementedException();
+		}
+
+		static IEnumerable<MethodBase> CheckIL( byte[] p, Module a, Type[] classGenerics, Type[] functionGenerics )
+		{
+			var position = 0;
+			var ret = new List<int>();
+			while( position < p.Length )
+			{
+				var opcode = OpCodeMap.GetOpCode( p, position );
+				position += opcode.Size;
+				if( opcode.OperandType == OperandType.InlineMethod )
+					ret.Add( BitConverter.ToInt32( p, position ));
+				position += OperandSize( opcode, p, position );
+			}
+			return ret.Select( t => a.ResolveMethod( t, classGenerics, functionGenerics ) );
+		}
+
+		static int OperandSize( OpCode opcode, byte[] p, int position )
+		{
+			switch( opcode.OperandType )
+			{
+			case OperandType.InlineNone:
+				return 0;
+			case OperandType.InlineMethod:
+			case OperandType.InlineField:
+			case OperandType.InlineType:
+			case OperandType.InlineTok:
+			case OperandType.InlineString:
+			case OperandType.InlineI:
+			case OperandType.InlineBrTarget:
+				return 4;
+			case OperandType.ShortInlineBrTarget:
+			case OperandType.ShortInlineI:
+			case OperandType.ShortInlineVar:
+				return 1;
+			case OperandType.InlineSwitch:
+				var numSwitchArgs = BitConverter.ToUInt32( p, position );
+				return (int)( 4 + 4 * numSwitchArgs );
+			case OperandType.ShortInlineR:
+				return 4;
+			default:
+				throw new NotImplementedException("Unsupported: {0}".F(opcode.OperandType));
+			}
+		}
+	}
+
+	static class OpCodeMap
+	{
+		static readonly Dictionary<byte, OpCode> simpleOps = new Dictionary<byte, OpCode>();
+		static readonly Dictionary<byte, OpCode> feOps = new Dictionary<byte, OpCode>();
+
+		static OpCodeMap()
+		{
+			foreach( var o in typeof( OpCodes ).GetFields( BindingFlags.Static | BindingFlags.Public ).Select( f => (OpCode)f.GetValue( null ) ) )
+			{
+				if( o.Size == 1 )
+					simpleOps.Add( (byte)o.Value, o );
+				else if( o.Size == 2 )
+					feOps.Add( (byte)( o.Value & 0xFF ), o );
+				else
+					throw new NotImplementedException();
+			}
+		}
+
+		public static OpCode GetOpCode( byte[] input, int position )
+		{
+			if( input[ position ] != 0xFE )
+				return simpleOps[ input[ position ] ];
+			else
+				return feOps[ input[ position + 1 ] ];
 		}
 	}
 }
diff --git a/OpenRA.Game/Game.cs b/OpenRA.Game/Game.cs
index c62296c236..1a0a288bc3 100644
--- a/OpenRA.Game/Game.cs
+++ b/OpenRA.Game/Game.cs
@@ -31,6 +31,7 @@ using OpenRA.Network;
 using OpenRA.Support;
 using OpenRA.Traits;
 using Timer = OpenRA.Support.Timer;
+using System.Collections.Generic;
 
 namespace OpenRA
 {
@@ -75,10 +76,19 @@ namespace OpenRA
 
 			// Mod assemblies assumed to contain a single namespace
 			foreach (var a in m.Assemblies)
-				if (Verifier.IsSafe( Path.GetFullPath(a)))
+			{
+				var failures = new List<string>();
+				if (Verifier.IsSafe(Path.GetFullPath(a), failures))
 					asms.Add(Pair.New(
-						Assembly.LoadFile(Path.GetFullPath(a)), 
+						Assembly.LoadFile(Path.GetFullPath(a)),
 						Path.GetFileNameWithoutExtension(a)));
+				else
+				{
+					Log.Write("Assembly `{0}` cannot be verified. Failures:", a);
+					foreach (var f in failures)
+						Log.Write("\t{0}", f);
+				}
+			}
 
 			ModAssemblies = asms.ToArray();
 		}