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I'm using Windows XP Professional SP2 on a single core AMD64 processor, and I've got two instances of MsMpEng.exe starting up when I start up and log in. They use 64MB and 32MB of ram and 140MB and 80MB of virtual memory, and fluctuate around 80% CPU usage for about 5 minutes at start up. They are (I read) associated with Windows Defender, but I'm concerned about:

  • There's two of them, everything I read generally has only one reported.
  • They might be scanning each other, and I want that to stop.
  • They might be getting scanned by avgrsx.exe (AVG Free 8) (uses about 16Mb v ram)
  • They might also be scanning moe.exe (assosciated with ms live mesh, which I'm considering getting rid of)
  • Lastly I have Microsoft Security Essentials. I don't know the process name associated there.

The main concern of mine (apart from the double instances) is that these are all trying to prioritize scanning each other at once except maybe moe.exe. This might seem legitimate but is likely a useless drain on resources.

Have I made a mistake in having all of these installed, or is there a way to inform them not to do whatever they're doing that's taking about 5+ minutes at start up? [I also have Google Desktop, but I'm keeping that.]

Comment if none of this makes sense to you.

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up vote 2 down vote accepted

While I haven't any answers for you (yet; update below), I can report that I'm seeing the same behavior on Winxodws XP Home / SP3 / 2.8ghz Intel Prescott. I've uninstalled AVG entirely, thinking that perhaps MsMpEng.exe (MSMP) was conflicting with antivirus software I hope to not even need going forward.

Startup time has slowed to a crawl. And I'm now seeing stalls when I open a file dialog (upload file, open file, etc.) when I attempt to scroll the list of files. WTF?

Two instances of MSMP are now always running, consuming 47mb (64mb vm) and 64mb (125mb vm).

Overall, Microsoft protection seems to be the kind of resource hog that drove me away from Norton/Symantec to AVG several years back. If this doesn't improve, I'll return to AVG Internet Security.


I have achieved a massive improvement in performance since my original post yesterday. Turns out I had Windows Defender installed and running alongside Microsoft Security Essentials. Uninstalling Windows Defender and rebooting took care of the unexplained second instance of MsMpEng.exe. The single instance running is now consuming 30mb less RAM -- 75mb (140mb vm).

I do not know whether this also helped, but I noticed two instances of ati2evxx.exe running -- this is a hot-key polling app for ATI video cards (Radeon X1550/512mb). I don't use it, removed it from Services and renamed the file to ~\Windows\System32\ati2evxx.exe.old

This machine hasn't performed so smoothly since I bought it with nothing installed! My Intel Pentium 4 521/Prescott (2gb ram) is barely working while running iTunes, Firefox 3.5.5 (15 tabs), Dopus/ExpanDrive (two remote SSH volumes mounted, 12 tabs open per vol) and PSPad Editor (22 tabs/files open). That pesky "scroll in file dialog" issue I mentioned earlier is now gone.

While this does impress me, I can also report that when MS Essentials commenced my nightly Full Scan with Real-time protection On, I noticed no significant degradation in performance! Even AVG commanded nearly all available resources for this kind of scan.

Crazy cool -- now if this actually protects my machine as well as AVG did for 4+ years, I'd say I'm done with third party antivirus protection.

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Yeah, WTF indeed. – dlamblin Nov 19 '09 at 23:35
Thanks for the Update, You would think MS would uninstall defender if it is superseded and partially conflicts with security essentials, when the latter is installed. – dlamblin Dec 14 '09 at 8:21

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