Until August 2002, the range of IP addresses from was reserved for future use. The unassigned or reserved IP addresses have been used in the past to perform Denial of Service (DoS) attacks. A number of ISP’s as well as Firewall operators decided in order to help limit the effects of these on their network they would perform filtering of the reserved space.

But,until august 2002. Since that time the address space has been used by ARIN for deploying new ranges to ISP’s. And,yes,most of people like me build a firewall script, grab the reserved and unassigned list from ARIN and build this list in to the firewall to never update it again.
At least, I know I had to update my firewall-scripts,

Read more about it on: <a href =”http://puck.nether.net/~jared/papers/69-paper.html” target=_blank>The problem</a>