Western Digital says the decision to block sharing of music and audio files is an anti-piracy effort.
The ban operates regardless of whether the files are copy-protected, or a user's own home-produced content.
Digital activists say it is the latest step in a so-called war on copyright theft that is damaging consumer rights.
The shift to a digital world in which all forms of content, from books, music, and TV programmes to films, can be shared effortlessly around the world between people with an internet connection has produced an unprecedented upheaval in attitudes to media, copyright and consumer rights.
Professional content producers have struggled to adapt to this changing world and deal with rampant copyright infringement that threatens to undermine their businesses.
The most popular method of copyright control in the digital age, Digital Rights Management (DRM), is a software - and sometimes hardware - solution designed to prevent copying and to control how different forms of media are used.
Peter Brown of the Free Software Foundation, a leading anti-DRM campaigner, said: "DRM and filtering attempts by firms like Western Digital are an attempt to take control of our computers.
"DRM is bad for society because it attempts to monitor what we do and how we live our digital lives. It is asking us to give up control of something which gives us some degree of democracy, freedom and the ability to communicate with a large group of people."
Western Digital has blocked users from sharing more than 30 different file types, if they are using the company's software, called Anywhere Access.
Mr Brown added: "DRM is never right because it takes away our rights as citizens."
He said all DRM solutions had been bypassed, rendering the technology useless.
"You can't stop the copying of ones and zeroes - its impossible," he said.
Paul Garland, head of intellectual property litigation at law firm Kemp Little, said it was not possible to say DRM was not working.
"Content creators are struggling to find a way to prevent mass distribution of their creations."
Alexander Ross, a partner at law firm Wiggin, said: "There is fundamentally two types of operation for DRM - to restrict usage, and track usage.
"That second element is essential and will remain essential - particularly for subscription services, which are beginning to take off.
"If we go down the subscription route, there must be control."
The common problem with DRM for many users is one of a lack of interoperability. Many of the world's leading content producers use DRM systems which are incompatible with one another.
The popular example is the majority of music bought and downloaded from iTunes, the world's most popular online music retailer, which can only be played in its original form on iPods, machines running iTunes and Apple's own wireless TV system.
However, iTunes does now sell a selection of music from EMI without DRM.
The BBC has been criticised for using a form of DRM for its TV downloads that means the programmes cannot be played on Apple Macs and PCs running Linux.
"The reason for a lack of standards across the industry is that there's no such thing as the industry," said Mr Ross.
"There is Steve Jobs and Microsoft and the two titans are at odds with one another. Between them they rule the market."
Mr Garland said: "The biggest problem is that it is actually quite difficult as a consumer when downloading content to know what you are able to do with it.
"If DRM is going to survive, there needs to be much greater effort to tell purchasers what they can or can't do with it."
Mr Ross said people had to understand they did not have the rights to do whatever they wanted with digital content.
One solution could be to develop information standards to inform people about the rights and restrictions around DRM, said Mr Garland.
He said: "Content owners are entitled to give you what rights they decide to give you; when you are downloading a piece of music, for example. They are also entitled to restrict you from circumventing the DRM.
"Trying to circumvent the DRM is an offence in itself. DRM is part of the law and a legitimate method of trying to protect your copyright content."
For the music industry the future looks less and less likely to involve DRM, said Mr Garland.
He said: "There is a backlash, people are concerned. The music industry is now talking a lot more about DRM-free products. DRM hasn't been the way to overcome the copyright infringement problem."
Mr Ross said that DRM as a copy protection tool might not last much longer.
"However, DRM as a track and rights management system is here to stay - as long as the music industry exists on a royalty model," he said.
Mr Brown said the industry did not need to use DRM, nor employ laws which prohibit the bypassing of DRM, in order to protect their financial interests.
"Media companies are trying to force people to think about copyright infringement almost in line with murder on the high seas.
"Copyright law is about copying and reproduction of work; that is on the statue books for everyone and is sufficient to tackle the problem.
"Digital restrictions management...is a restriction of our rights and the use we make of media files, that historically and legitimately we have been used to.
"The idea this is somehow protecting someone is untrue - it is an attack on us as citizens."