Hi, Microsoft Antimalware (Microsoft Security Essentials) completely stops its runtime protection while the program thinks the program itself or its definition is out of date. This is quite unexceptable because it turns out protection against older threads. I expect that the engine do its best to protect the computer even it finds itself or the definition out of date. Furthermore, the engine finds it out of date after start-up even after having the computer off over one night, or while the computer is alive and online over the midnight. The corresponding event in the event log is: Microsoft Antimalware Real-Time Protection feature has encountered an error and failed. Feature: Behavior Monitoring Error Code: 0x80004005 Error description: Unspecified error Reason: The filter driver requires an up-to-date engine in order to function. You must install the latest definition updates in order to enable real-time protection. I experience this logs quite often on Win7 x64 with Microsoft Update enabled to install automatically. The machine is always connected to the internet while running. The issue most often occurs for several seconds or minutes after starting the computer up. Usually, after few minutes the engine downloads updates from Microsoft automatically and than starts the protection. However, for the first few minutes, the computer is not protected, nor using the older definition nor engine. I rate this as quite critical design flaw or bug which is not acceptable for antimalware protection software.

Hi download the offline definition updates for MSE from Microsoft: Download for 32-bit Download for 64-bit apply the update and check if you can activate realtime protection again. André"A programmer is just a tool which converts caffeine into code" CLIP- Stellvertreter http://www.winvistaside.de/

Hi, the automatic definition download seems to work correctly. It just takes time after computer start-up to initialize Windows Update, search for it and download them. However, until it completes, the engine refuses to start and leaves the computer unprotected.

Hi, Thanks for posting in Microsoft TechNet Forum. I suspect this is caused by software conflicts. Do you have another program which provides real-time protection? If so, please turn it off. If the issue persists, you can reinstall Microsoft Security Essentials to check the result. Since this is related to the specific application, we would like to advice the following forum discussion for your reference: Microsoft Security Essentials: Updating Virus and Spyware Definitions Forum The reason why we recommend posting appropriately is you will get the most qualified pool of respondents, and other partners who read the forums regularly can either share their knowledge or learn from your interaction with us. Thank you for your understanding. Hope it helps. Alex Zhao TechNet Subscriber Support in forum. If you have any feedback on our support, please contact tngfb@microsoft.com Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.

Hi, If you have other questions, please feel free to let us know, we are willing to help you. Have a nice day. Alex Zhao TechNet Subscriber Support in forum. If you have any feedback on our support, please contact tngfb@microsoft.comPlease remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.