Somewhat similar to the typo squatting story earlier, the recent proliferation of cloud service usage by enterprises has led to a new problem. For a project at a community college, we needed a couple servers, and didn't want (or have the funds) to build them on-site. In view of the limited duration of the experiment, we decided to "rent" the boxes as IaaS (infrastructure as a service) devices from two "cloud" providers. So far, all went well. But when we brought the instances live, we discovered to our surprise that three (out of 24) public IP addresses that we were assigned still had "afterglow", meaning they were receiving productive traffic that was intended for the former owner/holder of these IPs. Two of the IPs received DNS queries, one was receiving email. Researching through the passive DNS logs, I confirmed that yes, the three IP addresses had indeed been used accordingly. One of the DNSes had been active only for a week, obviously for nefarious purposes, because it had lots of random .ua and .pw domain names delegated to it. The other seems to have been the DNS+EMail of a midsize company that had been hosted with that IaaS provider for two years, and had been migrated elsewhere earlier that same week.

To make a long story short, for all services where the Internet has an extended memory and caching, make sure you hold on for a couple of weeks or months to the corresponding IP or domain name after you no longer need and use them, and let them "cool off". Otherwise, if the IP address is immediately reassigned, or the domain name immediately repurchased, someone else *will* end up with some of your web traffic, DNS requests, or even email.