[runjake]

Seemingly harmless data on victims can be assembled into a big picture from disparate sources.

A particularly-common example are website security questions ("What high school did you graduate from?", "Who's your favorite musician?", etc). The answers to these questions can often be assembled from open sources. If I happen to have your email address and something like a bank account #. I can search a variety of sources and come up with more information (mother's maiden name, see who your fav artist is on Facebook, etc). Up until recently, it was very easy to use the security question attack on Yahoo and Gmail accounts, and as you probably know, there's often a treasure trove of info in someone's email account.