Android apps are passing data to advertisers across the EU, including here in the UK.
Viviane Reding, Vice President of the European Commission told Channel 4 News on 4 March: "They are spotting you, they are following you, they are getting information about your friends, about your whereabouts, about your preferences."
MWR Infosecurity, a firm which Channel 4 News commissioned to investigate the apps, said: "We found that a lot of the free applications in the top 50 apps list are using advertising inside the applications and that the permission that you grant to these applications is also granted to the advertiser. If users knew about this I think they would be concerned about it but at the moment I don't think they are aware of the situation and how widely their information can be used."
The illegal privacy breach affects one quarter of all UK mobile users.
The breach occurs when Android users, who downloaded 100,000,000 Apps in January alone, grant apps permission to access certain features on their phone. The permitted information is then "handed on" to advertisers.
MWR Infosecurity found a line of computer code that gave advertising networks access to contacts, calendar and the phone's location.
The code came from a large US advertising network called MobClix.
Channel 4 News took its findings to Reding, who is working to reform EU-wide data protection legislation.
Reding added: "This really concerns me, and this is against the law because nobody has the right to get your personal data without you agreeing to this. Maybe you want somebody to get this data and agree and it's fine. You're an adult and you can do whatever you want.
"But normally you have no idea what others are doing with your data. They are spotting you, they are following you, they are getting information about your friends, about your whereabouts, about your preferences. That is certainly not what you thought you bought into when you downloaded a free of charge app. That's exactly what we have to change."
Google, which runs the Android system, told Channel 4 News that it has best practises for app makers to follow when it comes to user data. Crucially, it doesn't screen applications before they are offered for download.
At Mobile World Congress last week, Android was launched as the operating system in the new Panasonic Eluga waterproof phone.
Eric Schmidt, Google's executive chairman proudly told the assembled audience for his keynote address that 300 million Android devices are currently activated, 850,000 more are activated each day and 1 billion apps are downloaded a month.
In 1999, Sun Microsystems Inc. CEO Scott G. McNealy said: "You already have zero privacy. Get over it." But we haven't, and it doesn't look like we will any time soon.