For those who like to keep abreast of security issues, there are interesting developments happening at BlackHat with regards to Cisco IOS and its vulnerability to arbitrary code executions.
I apologize for the article itself being brief and lean on technical details, but allow me to say that it does represent a real problem (as in practical and confirmed):
http://blogs.washingtonpost.com/securityfix/2005/07/mending_a_hole_.html
