Microsoft Security Essentials is a real-time protection system that will protect your computer from all kinds of malware - like viruses, rootkits, and spyware - by analyzing your computer and alerting you whenever it detects unfamiliar and potentially dangerous elements. It detects malware by consulting its huge database which is constantly and automatically updated. You can use it without an Internet connection, too, so it can analyze your computer even if it's not online. It also consumes very little resources, unlike antivirus suites made by third parties. This makes Microsoft Security Essentials an ideal solution since it won't affect the use of your computer while it works.
The program is divided into several sections: analysis, upgrade, history, and configuration. If you don't have much experience, you can focus on the first two. In the history section, you can check what was found when your computer was analyzed. It shows the detected items, quarantined items, and allowed items. In the configuration section, you can schedule scans, automate tasks, modify protection options in real time, add files and folders to the exclusion list, and edit advanced antivirus settings.
For all these reasons, Microsoft Security Essentials is a great choice if you're looking for a free, lightweight, and reliable antivirus software.
Windows Defender is included by default in Windows 8, 81. RT, and 10, so it's not necessary to install it if you have any of these versions.