Spammers can only operate for so long before they're found out and shut down . Once eradicated, they leave a virtual ghost town behind them.
Scores of Internet addresses have been abandoned this way, says The Washington Post , creating eerie pockets of deadness that few legitimate businesses are willing to take over. If a spam host operates for long enough, its addresses become known to IT and security professionals, at which point IP addresses originating at that host get "blocklisted." But once an IP reaches a blocklist, it's rarely, if ever, revisited and considered for removal--no matter if the address now points to a legitimate entity.
The result has been ever more clever malware. Once spammers were privy to the vulnerability of their hosts, they began designing their software to distribute itself from a litany of hosts--a perversion of "cloud computing." Conficker, one of the most aggressive bot-net viruses built to date, works this way and has found its way onto an estimated 7 million PCs.
The solution might be a centrally-controlled block-list that could conflate and test the dozens of lists currently in circulation. But such a list could run into legal obstacles presented by the Commission's proposed net neutrality regulations, which might effect the ability of Internet providers to deprioritize  or block certain hosts.