Security risk vary depending on the distribution and the software you use... similar to any other OS or network device. Information Security
/ Information Assurance
applies to everything. You can find specific information on websites, registering on mailing list and even RSS feeds.
Everyones favorite Ubuntu!
This is how I found it.
http://www.google.com/search?hl=en&q=ub ... ubuntu+sec
http://www.google.com/search?hl=en&q=ge ... tnG=Search
http://www.google.com/search?hl=en&q=op ... tnG=Search
Here's a few examples of some well known software.
http://www.mozilla.org/security/known-v ... refox3.0.5
The good news is that Package Managers take most of the fun out of all this. These two commands update my entire system... with the exception of a few programs I compiled and installed myself.
sudo apt-get update
sudo apt-get upgrade -y
KDE has this nice GUI front end that does the same thing... and a whole lot more.
Websites like http://www.linuxsecurity.com/
can help keep people informed too. The use of firewalls, file encryption and access controls are important and often overlooked. Common Sense is always a killer too.