One of the best antivirus software in the market which protects the computer system from various malicious intrusions such as spyware, viruses, Trojans and rootkits extremely effectively is Microsoft Security Essentials, stylized as MSE. Microsoft Security Essentials was initially released on the 29th September, 2009. It works as an intrusion detection system as well as an antivirus system. As per the license agreement, the Microsoft Antivirus free version is allowed to be used by small businesses and home users. Microsoft Security Essentials replaces both, the free Windows Defender that protected the users from spyware until Windows 8 was launched, as well as Windows Live OneCare, a subscription-based antivirus product that was commercially discontinued.

The construction of the Microsoft Security Essentials program is the same as other antivirus products and scanning engines that have been developed. Microsoft Security Essentials also provides facilities and features such as real time protection that constantly keeps a check on the system, scanning of the new files as and when they are either downloaded or created and also disabling unavailable threats which it detects. However, not all good things come together all at the same time. The same goes for Microsoft Security Essentials. The antivirus lags behind as it does not have OneCare personal firewall and Forefront Endpoint Protection.

The antivirus industry expressed a set of mixed reactions when Microsoft, on the 18th of November 2008, announced the release of their own antivirus software. Avast software and AVG Technologies appreciated the initiative taken by Microsoft to launch Microsoft Security Essentials providing the consumers with another name and another choice of antivirus software that they can consider. However, industrial giants such as Symantec, Kaspersky and McAfee considered Microsoft Security Essentials not to be a competition or a threatening rival.

The positive reviews received by the Microsoft Security Essentials are generally for its user interface, freeware license and low resource usage. In a test conducted in October 2009, Microsoft Security Essentials eliminated all popular and existing malwares. Thereafter, the scoreboard of the outcomes of the tests performed on Microsoft Security Essentials revealed poor scores after which Microsoft took up the task of improvising their product. In the last couple of years, the software has attained a 100% in detecting all the malware samples used to conduct the test and was regarded on top of the charts.

According to a report published by an anti-malware specialist in March 2012, Microsoft Security Essentials was considered to be the best antivirus service product in North America and the 2nd most-wanted antivirus product across the globe.

The latest virus database is downloaded and checked automatically by Microsoft Security Essentials, through the Microsoft Update. The virus definitions are updated by Microsoft Update 3 times in a day.

Microsoft Security Essentials is available in various languages such as simplified as well as traditional Chinese, Dutch, French, Latvian, Latin Serbian, Greek, Croatian, Italian, Portugal and Brazilian Portuguese, Korean, Turkish, Russian, Danish, German, Thai, Slovak, Polish, Japanese, Estonian, Finnish, Ukrainian, Romanian, Spanish, Czech, Vietnamese, Swedish, Lithuanian, Norwegian, Hungarian, Bulgarian and English.

Microsoft Security Essentials detects threats and immediately notifies the user to get an input as to how the detected threat is to be dealt with. If the user doesn’t respond within 10 minutes, the detected threat is dealt with as per the actions that are default which are specified in the settings of the application. As per these settings, System Restore checkpoints may also be created before the detected threat is removed. As a default action, all behaviors detected as ‘suspicious’ by Microsoft Security Essentials are reported to Microsoft Active Protection Service. If such a report matches any recently discovered threat with a virus definition that is not yet released, then a new definition will be required to be downloaded to remove the threat.