Probably: c:\Windows\System32\mspatchc.dll = Microsoft Patch Creation Engine Code: CreatePatchFileA CreatePatchFileByHandles CreatePatchFileByHandlesEx CreatePatchFileExA CreatePatchFileExW CreatePatchFileW ExtractPatchHeaderToFileA ExtractPatchHeaderToFileByHandles ExtractPatchHeaderToFileW GetFilePatchSignatureA c:\Windows\System32\mspatcha.dll = Microsoft File Patch Application API Code: ApplyPatchToFileA ApplyPatchToFileByBuffers ApplyPatchToFileByHandles ApplyPatchToFileByHandlesEx ApplyPatchToFileExA ApplyPatchToFileExW ApplyPatchToFileW GetFilePatchSignatureA GetFilePatchSignatureByBuffer GetFilePatchSignatureByHandle