It's Google Maps, cross-referenced with a bunch of databases, PLUS:
"Can I help by suggesting someone who needs to be listed?
Yes you can! Just use our contact page, and we’ll get them added in a hot hurry. Usually we verify it, but usually we don’t have the needed time or resources to insure it is valid. Please use this tool with honesty and integrity."
I haven't checked 1600 Pennsylvania Avenue in DC yet.
UPDATE: It seems this is an all-too-convincing hoax. See for yourself by trying an address more than once. The results change.