Note: other spam researchers prefer to use a percentage of IPs that are listed in a subnet.
Using percentages is better suited for "unclean" subnets because "clean" nets have significantly less than 1% of addresses listed.
The CBL DNSBL (Composite Blocking List) lists IP addresses that are compromised by a virus or spam sending infection (computer worm, computer virus, or spamware).
[2] The CBL Index is a reasonably good tool for getting estimates of subnet "outgoing spam reputation".
The CBL Index for the net was: 2_097_152/166_086 = 12.6 (*/28.3 ; 11.0 dB) 2_097_152 – number of IP addresses in */11 network (2**(32-11))