This is where it is sorta tricky. This part has been interpereted to say that anytihng found durign a reasonable execution (aka, no searchign in pill bottles for stollen TVs) of a warrent is admissable. The rule for physical searches is "in plain sight". If the police are searching your home for, say, a fugitive, and you have a bong on your table, that's in plain sight. Data mining is the exact opposite. It's taking a microscope to any minute detail you can find, but strip-searching not just an individual home, but an entire neighborhood. That's the kind of physical search that's explicitly prohibited. Does the principle apply to wiretaps? You'd think so.