Internet Security Suites are enhanced security application with added protection like Anti Rootkit, Anti Identity Theft or Firewall which are usually missing in the Antivirus Suite. most of the free Internet Security Suites available are the downgraded version of the paid counter parts, often without realtime scan/shield feature in it. for an security application, realtime shield/scan is the foremost and outmost feature which makes the Antivirus or Internet Security Suite vigilant to virus eruption in realtime and also to work as a standalone security tool. Here's a list of 5 free Internet Security Suite for home/corporate use. FortiClient Endpoint Security Standard Edition and Spyware Terminator with ClamWin Antivirus are also available free for Corporate use. 
1) Comodo Internet Security Suite
Well suited to the need and innovative security suite with full featured and sandbox technology to detect the latest threats and viruses. Free ones doesn't come with live tech support. Totally free for home use.
2) CyberDefender Early Detection Center
Initial known as CyberDefender Internet Security Free. It was ad supported then. I did try it once. I didn't find it to be a decent application coz it just couldn't prevent the drive by download rogue application which eventually happend to be a trojan. It just failed to do the work. since then I uninstalled it. though the site boast of being a legit security tool with links to various download portals like C-Net, soft32, SoftPedia, Brothersoft etc.
. It also can clean in AVG Link Scanner. May be an enthusiast must have look at this application
3) Ad-Aware Free Internet Security
Its an upgraded version of Ad Aware Free AntiMalware, with built in basic realtime shield. Loyal Ad Aware Free AntiMalware users can now step up their security level which eventually was without a real time shield. Totally free for home use only.
4) FortiClient Endpoint Security Standard Edition
A standalone free security tool for corporate use. It has antivirus, antispyware, antirootkit, antispam, web filtering, firewall and VPN support too. Installer is mere 12 MB size. for product support and WAN optimizing, you'll need to buy a Premium edition.
5) Spyware Terminator With WinClam Antivirus
By default Spyware Terminator doesn't come with WinClam Antivirus and web shield, you'll need to download the application after the full installation. Totally free for home and corporate use. the advantage of using this application is that WinClam Antivirus is tailored to the realtime shield of this application. even the standalone ClamWin Antivirus doen't come with realtime shield in it.
Related Posts: ANTIVIRUS,WINDOWS 7
5 Free Internet Security Suites For Home/Corporate Use