On the top floor of a nondescript building in Toa Payoh, an army of workers is busy mining your personal details. Some are on the phone, negotiating a price for bundles of people's personal information. Others are handing over documents with names and addresses to buyers in exchange for cash.

They are part of a cottage industry of at least half a dozen companies here making money from dealing in others' data - full names, home addresses and phone numbers - raising questions about whether what they do is legal.