Alright so I was testing out a new tool for building backlinks, and I had all the links pointing back to a junk domain that I own. This was a worthless domain that I never had any intention of ranking with, so I didn't care whether or not it got sandboxed. I left the tool on overnight and by morning it had built around 5000 backlinks. A couple days later I decide to check my rankings with my Rank Tracker tool, and not only is the junk domain sandboxed, every single domain I own is as well! None of the domains are deindexed, but all of the hundreds of keywords that I had ranking on the first page of Google are now on like page 6. How did this happen? I'm not too concerned with being sandboxed, as I'm sure my rankings will return to normal relatively soon, but I'd like to know how Google linked all the sites together, and how I can prevent this in the future. The junk domain did NOT have Analytics or Adsense on it, or Google Webmaster Tools set up, and all of my domains have WhoIs Guard enabled, so Google couldn't have linked the sites together that way. The only thing that the sites have in common is that they are all on the same shared hosting account, but I assume that tons of people must be on the same hosting servers, so how could Google possibly penalize all of them? I mean, if someone spams a subdomain on wordpress.com, Google wouldn't penalize every single wordpress.com subdomain, right? So how did they know exactly which sites to sandbox? Any help is much appreciated.