Can Windows Defender & Microsoft Security Essentials Run at the Same Time?

By James T Wood

Keep your Windows computer protected with security software.
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Microsoft released different security programs to provide protection for users of the Windows operating systems from malicious attacks through spyware, adware and computer viruses. Windows Defender was released to protect against spyware and adware, but not viruses. Microsoft Security Essentials (MSE) was designed to protect against viruses in addition to spyware and adware.

Spyware and Adware

Software that runs on your computer without your permission and reports your activities to a central location is known as spyware. It is installed on your computer without your permission, often through a link from a website or by inclusion in the installation package of another piece of software. Adware is software that runs on your computer to deliver ads to you. It is usually installed on your system in a similar way to spyware without your knowledge or consent.


Computer viruses are malicious programs that replicate and resend themselves to other computers. Viruses infect your computer through a plethora of sources including infected websites, infected downloads and infected emails. Once infected, your computer may be used to redistribute the virus or for some other purpose of the virus maker's intent.

Microsoft Defender

In order to protect against spyware and adware, Microsoft released the free Microsoft Defender program (see "Resources"). Since 2006, the software has been offered to owners of Windows computers with a valid license for the software (i.e., not pirated software) to help prevent the infection of computers with unauthorized software.

Microsoft Security Essentials

In 2009, Microsoft released MSE to provide anti-virus protection, which scans computer activity in real time to prevent infection from a computer virus (see "Resources"). MSE constantly updates the definitions by which it determines what a virus looks like so that your computer can be protected against the most cutting edge virus threats. MSE also incorporates the spyware and adware protection from Microsoft Defender. The two programs are not compatible, and MSE is designed to disable and/or uninstall Defender. Microsoft Defender is intended for use on systems that are not using MSE as an anti-virus solution.