Microsoft Security Essentials is an anti-virus for Windows XP (IA-32), Windows Vista, and Windows 7 (both IA-32 and x64). It is designed for consumers and lacks centralized management features which are found in Microsoft Forefront Client Security. It replacesWindows Live OneCare, a commercial subscription-based antivirus service and the free Windows Defender, which only protected users fromadware and spyware.

Microsoft Security Essentials includes the same anti-malware engine (dubbed "Microsoft Malware Protection Engine", or MSMPENG for short), and virus definitions that all other Microsoft desktop anti-malware products share, including Forefront Client Security, Windows Live OneCare and Windows Defender. Before installation, Microsoft Security Essentials checks for the validity of the installed copy of Microsoft Windows. Microsoft Security Essentials requires no registration or personal information. Microsoft Security Essentials disables Windows Defender, since Microsoft Security Essentials also provides protection against spyware and adware.

Using default settings, archived files are decompressed, and then scanned. File downloads and e-mail attachments are also scanned. Its Dynamic Signature Service attempts to better identify malicious files by checking for updates if an application exhibits suspicious behavior. Before taking action against a suspect file, Microsoft Security Essentials prompts for user input. If no response is received in ten minutes, then the suspected malware is handled according to its default action, letting Microsoft Security Essentials determine what to do with the malware. System Restore points are created before removing found malware.

Microsoft Security Essentials automatically checks for and downloads virus definition updates which are published three times a day toMicrosoft Update. Alternatively, users may download the updates manually from Microsoft Security Portal.

Download Microsoft Security Essentials version 4.0 beta

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