Satellite television company Sky says it is probing the use of digital boxes to hack its signals.
Receivers are being advertised by a Dundee Facebook user. The devices allow the user to get all satellite channels without paying subscription fees.
The so-called open boxes require users to have a satellite dish but not an active subscription.
It is not illegal to own these boxes as on their own they only give access to free-to-air channels.
They can also be used to stream content from the internet.
However, it is against the law to use one that has been pre-configured to hack subscription channels by using codes purchased online to decode the signals.
One local man on Facebook was offering to sell and install the boxes for £120 even though they are available to buy online for less than a third of the price.
His advert said: “These are satellite boxes with ALL uk sky channels and all packages inluding SPORTS, MOVIES, MUSIC, DOCUMENTARIES, KIDS, LIFESTYLE & SKY BOX-OFFICE.”
He also says buyers will need to spend £25 a year to reboot their system.
When approached by a Courier reporter posing as an interested buyer, he said he could install the device within 48 hours.
He said: “It’s basically plug in and go. They are £120.”
Asked if the set-up was legal, he said: “Wouldn’t say Sky would be happy if they knew everyone had these but who’s honestly going to know unless you have the chief executive in your living room?
“It’s either £120 one-off or £60 to £100 every month for your normal bill.
“You must have a Sky dish though and internet connection. Doesn’t matter if you’re not with Sky any more as long as the wire still comes into the house from the dish.”
A Sky spokeswoman said the company would pursue anyone who illegally accesses their services.
She said: “We strongly advise people not to buy products or services which on their own, or in combination with codes, claim to offer access to Sky content.
“Such services are not authorised by Sky and are unlawful, and those who buy them could find their service switched off at any time.”
Four years ago, a gang of three London men who supplied 400,000 boxes that let people watch Virgin cable channels for free were jailed for 15 years.
Following the prosecution, the Metropolitan Police warned that anyone who uses an illegal box could also be charged.