How does ANY business find info about you and where you have been on the net and what you have done??? Think cookies, spyware, trojans, active-x etc. etc. ad naseum.
Nirvana,
Guns has already explained it but there is no CONSTITUTIONAL protection from private spying on you. The CONSTITUTION limits or enables the FEDERAL GOVT. in whatever actions they do or contemplate. Much later after the constitution was written, court decisions interpreted the constitutional protections / limitations also apply to state and local government actions, not businesses or private individuals.
The protection from private sources of "spying" are the state and local laws and limited federal laws regarding interstate communications. In other words if a private investigator is "spying" on you it is not a constitutional issue, it may be a burglary issue but not a 4th ammendment issue.