A number of ESPs have been tracking problematic signups over the last few days. These signups appear to be coming from an abusive service called SpamZa.
SpamZa allows anyone to sign up any address on their website, or they did before they were unceremoniously shut down by their webhost earlier this week, and then submits that address to hundreds of opt-in lists. This is a website designed to harass innocent recipients using open mailing lists as the harassment vehicle.
Geektech tested the signup and received almost a hundred emails 10 minutes after signing up.
SpamZa was hosted on GoDaddy, but were shut down early this week. SpamZa appears to be looking for new webhosting, based on the information they have posted on their website. 
What does this mean for senders?
It means that senders are at greater risk for bad signups than ever before. If you are targeted by SpamZa, you will have addresses on your list that do not want your mail. Some of those addresses could be turned into spam traps.

1. Check your signups. If you see hundreds of signups coming from the same IP address over a very short period of time, treat them carefully. There are a number of things a sender can do to limit the impact on a list.
   1. Delete the addresses coming from a single IP
   2. Confirm the addresses coming from a single IP
2. Implement confirmation. Start using closed loop opt-in (double opt-in) on new signups going forward. This will keep future incarnations of SpamZa from corrupting a list. It will also prevent lists from acting as attractive nuisances.
3. Do not trust vendors. Senders who are are buying a list or using a co-reg provider must confirm all the addresses before mailing them. There are some suggestions that the SpamZa people are selling addresses. Senders must protect themselves and their assets.

The one thing a sender absolutely does not want to do is add any SpamZa collected addresses to a mailing list. This is not a problem that will go away, it is out there in the wild now. This is the time to start implementing protections, not after the horse has left the barn. Confirmation is one of the better ways to protect an asset against this type of interference.
Followup post: Yet More Data Verification

Confirmed (double) opt-in • harassment • Spam