[cyanbane]

Naive question, but how much of this information could be gleamed by a nefarious source from an aluminum can you throw away or a piece of hair you drop?

[gwern]

Enough to convict you in a court of law - cops do it all the time. (It's not a search requiring a warrant if you throw the cup away, it turns out.)

[cjbprime]

All of it.