Federal regulators are letting cable companies scramble all their TV signals, closing a loophole that lets many households watch basic cable channels for free.

The Federal Communications Commission voted Friday to lift a ban on encryption of basic cable signals, saying it will reduce the number of visits by cable technicians to disconnect service and reduce cable theft.

The change will also affect households that pay for TV but have some sets hooked up directly to cable, without set-top boxes. They will need to get boxes for those sets.

Neither the FCC nor the National Cable & Telecommunications Association knows how many households are taking advantage of the unencrypted signals or will need set-top boxes. NCTA spokesman Brian Dietz says most of the theft is by cable modem customers who also connect their line to a TV set.

Comcast Corp. and Time Warner Cable Inc., the two largest cable companies, could not say when they will start encrypting their basic signals.

Satellite TV providers DirecTV Inc. and Dish Network Corp. already encrypt all their TV signals. Cablevision Systems Corp., which mainly serves customers in the New York area, also does so, thanks to a waiver from the FCC. Cablevision has had relatively few complaints about the practice, the FCC noted in its decision.