Defender is an antivirus program available at a lower price than other products, like Symantec, McAfee, etc. Recently, Defender has now been integrated with Kaspersky Labs. There are two variants available for this product, Home basic edition and Pro. It has features that all other antivirus programs have like anti-spam, URL syntax checking, Firewall, Anti-spyware, etc. Defender has one surprise feature though called Secret Surf, which leaves no trail of your browsing history. There is feature, like free update of Anti-spyware database, that most other common Anti-virus programs don't provide.
Room for Improvement:
The most problematic part of this program is the difficult customer service. Upgrading the software may cause a little bit of trouble. Your computer may lock down soon after your first reboot. There have also been some problems with the connectivity and with the internet, soon after the installation of the program. Trouble-shooting by Customer Support Engineer may take some time to figure out the problem and fix it. You may find your computer slowing down after installing the program.
Defender Pro or Home Basic antivirus provides some sort of security against the latest internet threats, but going for the reputed Anti-virus software like Symantec Endpoint, Quick Heal, etc. would be a wiser choice. The price of this program may be a bit lower, but safety of you and your computer is of greater importance.