An anonymous reader writes "The most comprehensive scan of the entire internet for several decades shows that millions of allocated addresses simply aren't being used. Professor John Heidemann from the University of Southern California (USC) used ICMP and TCP to scan the internet. Even though the last IPv4 addresses will be handed out in a couple of years, his survey reveals that many of the addresses allocated to big companies and institutions are lying idle. Heidemann says: 'People are very concerned that the IPv4 address space is very close to being exhausted. Our data suggests that maybe there are better things we should be doing in managing the IPv4 address space.' So, is it time to reclaim those unused addresses before the IPv6 crunch?"