I first read this on the NANOG list, but it appears to have been broken by BugTraq. According to this translation of the original Russian story:
"As it became known to SecurityLab, the source code of operating system
CISCO IOS 12.3, 12.3t, which is used in the majority of Cisco network
devices has been stolen on May 13, 2004. The total volume of the stolen
information represents about 800MB in an archive file."
The Russian site shows "ipv6_discovery_test.c -- Neighbor Discovery unit tests" and "ipv6_tcp.c -- IP version 6 support functions for TCP" as some sample code.
Update: This was my 500th Blog post.