Windows Defender Real Time Protection Service slowing down file access

Question

I noticed after a recent Windows 10 update that Windows Defender's real-time protection dramatically slows file system access. 

I timed how long it took to build a (Delphi XE6) project with Windows Defender's real-time protection off and on in order to get a sense of how bad it is.

 I did nothing but alternate between real-time protection off and on (no reboots required, physical hardware):

Trial	Real-time protection status	Build time (s)
1	On	86.4 s
2	Off	4.0 s
3	On	84.0 s
4	Off	4.0 s
5	On	86.9 s
6	Off	4.1 s
7	On	87.4 s
8	Off	3.9 s

Which means:

• Build time with real-time protection off:  4.0 s  (sd: 0.082 s)
• Build time with real-time protection on: 86.2 s  (sd: 1.51 s)

This means that Windows Defender in Windows 10 has now entered the realm of other crappy anti-virus products - that are a detriment to the user's PC rather than a benefit.

• Of course i'm not going to wipe my PC and reinstall everything.
• Of course there is no other anti-virus software installed.
• Of course i made no changes to this PC prior to this happening.
• Of course this is not a virtual machine.
• It spontaneously started Wednesday October 19.
• I have no idea what could have happened to my PC between 5pm on October 18th, and 9am on October 19th:

No idea whatsoever. 

Without disabling Windows Defender Real-time protection, how do I make Windows Defender not perform file-scans before an application attempts to open a file? That is: how do i make Microsoft's own anti-virus software as fast at it used to be in Windows Vista, Windows 7, Windows 8, Windows 8.1, and Windows 10 before a recent update?

Bonus Reading

This question has of course already been asked, and ignored, on these forums.

• Microsoft Answers: Windows Defender Real Time Protection Service slowing down Visual Studio etc.
• Stackoverflow: Windows Defender Real Time Protection Service slowing down Visual Studio etc
• Stackoverflow: Slow page refresh times during development
• Speed Up Visual Studio Build Times (by disabling Windows Defender)

***Post moved by the moderator to the appropriate forum category.***

Answer 1

Solution

The issue that is Windows Defender's Real-time protection is blocking an application from being able to read a file until it has read the file. It should, of course, be scanning in parallel - not synchronously delaying file access.

Fortunately, Windows Defender has the capability to skip synchronous checking of files based on a file extension - called Exclusions:

What you can do is under Windows Defender, click Add an exclusion. Under File Types, click Exclude a file extension. Individually add the extensions:

• pas - Delphi Source File
• dfm - Delphi Form
• dpr - Delphi Project
• dproj - Delphi Project File
• dcu - DCU file
• cs - C# source file
• txt - Text File
• pst - Outlook mailbox
• docx - Word document
• xlsx - Excel spreadsheet
• gif - Graphics Interface Format image
• jpg - Joint Photographic Experts Group image
• bmp - Bitmap
• res - Compiled resource
• bpl - Borland Package Library (a dll with a different extension)
• dll - Dynamiclly Linked Library
• exe - Application
• com - Application
• bat - Batch File
• cmd - Command file
• scr - Screen saver
• cpl - Control Panel Applet
• et cetera

This way you get all the security of real-time protection, with the blazing speed of unimpeded native file access performance.

This change improved my build times:

• Before: 86.2 s
• After: 4.7 s

A 94.5% improvement!

Answer 2

I'm surprised there aren't more comments on this. I just moved from OSX to start front end development on my desktop Windows 10 machine and this Antimalware Service Executable is crippling everything; especially when staging new repositories or unzipping stuff. I just unzipped a small archive; it took 3 seconds with real time protection off, and 20 with it on.

This is great, thank you. One question - this effectively stops Defender from ... defending ... your computer; if you're going to get a virus, won't it usually come in the form of .exe? Not all of the extensions in your post are safe to ignore.