Zillow knows about a default before its recorded

[Rich Hupper]

As many of you may know you can get pre foreclosure information from zillow.com. I generally never go to zillow this information because in my area the county recorder / registry offices upload everything to their respective websites. 

What confounds me is, today I get a call from a client about a property they saw on zillow listed in blue as a pre foreclosure. Thinking this information would be wrong or dated, I hop on the registry's website and begin searching. To my surprise there is no "order notice" recorded at the registry ( in Massachusetts this is the first document recorded when a mortgagor has been in default for 90 days ). 

My question is how does zillow know about properties in default before the registry of deeds does?