What is the Ubuntu "built in virus protection"?

At ubuntu.com there is this "only in ubuntu" that says "Built in virus protection":

What is the Ubuntu built it protection? What is the program in charge of this and how does it work?

"Built-in virus protection" is a simplification of the security features of Ubuntu.

• Ubuntu requires applications to be run as super-user to cause any damage. It also includes AppArmor to supplement that.

• There is also the safe and secure repository model which gives you access to thousands of applications through the Software Center which are tested by package maintainers.

• Since it is free software more people have access to the source code and according to Linus's law: "Given enough eyeballs, all bugs are shallow", which means that

  Given a large enough beta-tester and co-developer base, almost every problem will be characterized quickly and the fix will be obvious to someone.

• The security exploits are quickly patched up and delivered to you through the Update Manager.

My 2 cents are that it is possible to get a virus for Ubuntu, but:

• The way most Linux distributions are built make it very hard for virus/trojans/backdoors to take advantage of vulnerabilities in binary packages. Ubuntu changes every six months (and updates --sometimes annoying-- land at least every week). It makes it very difficult for a virus author to track all these changes. In contrast, windows takes several years to change. That gives some time to the virus author to try to be as destructive/invasive as it can.
• AFAIK, there is a substantial difficulty to "leak" binary code or suspicious source code to Ubuntu's Official or Debian's official packaging systems.
• There might be 3 ways to infect a Linux box:
  • You 've been running Linux for years without updating any of your internet-facing services/apps.
  • You installed a virus/trojan by yourself.
  • You downloaded the virus in source code, compiled it and ran it with administrator privileges ;)