If one address is notably probing vuylnerable port ranges, or constantly spitting at one port, then I'd report it here
http://www.ntlworld.com/netreport/
Sadly, "firewall reports" are not taken seriously by many, as a lot of firewall users have hyperactive alert settings and don't bother distingushing "background noise" from what is likely to be a virus probe against everyone on the same segment or more.
The golden rule, unless YOU have upset a script kiddie somewhere, YOU are not important enough for even a novice grade hacker to bother with, though cable modem address ranges are popular with anyone looking for a trojanized system, as they would provide a fast and powerful service as the next spam delivery agent - there's **** profit in trojans now!