Data from several Android apps automatically sends data to Facebook - even if the user does not have an account with the social media giant.

Apps such as Yelp, Indeed and Duolingo automatically send user information to the company when an Android user opens the app.

This flaw was first pointed out by Privacy International in December when an investigation found 23 popular apps all did the same thing.

Most firms, including Spotify, Skyscanner and Kayak, have since corrected the issue but a handful have yet to rectify the privacy concern, the report claims.

It is also believed the apps for Apple iOS devices also 'exhibit similar behaviour'.

Facebook and Privacy International have since had discussions in a bid to address and resolve the issues raised by the charity.

Scroll down for video

In lengthy blog post on Wednesday, CEO Mark Zuckerberg detailed a plan to bring end-to-end encryption to Messenger, WhatsApp, and Instagram messaging services – confirming previous reports that the firm planned to stitch the three together. File photo

The London-based charity revealed Yelp, Duolingo, Indeed, the King James Bible app and two Muslim prayer apps, Qibla Connect and Muslim Pro, send personal data to Facebook before users can decide whether to give consent or not.

Privacy International claims it raised the issue with the European Data Protection Board and the European Data Protection Supervisor.

The charity says the data is transmitted due to the setup of Facebook's Software Development Kit (SDK) – a Facebook business product that apps integrate into their code.

It is designed to automatically transmit personal data to Facebook when an app is opened.

A Facebook spokesperson told MailOnline: 'Facebook's SDK tool means that developers can choose to collect app events automatically, to not collect them at all, or to delay collecting them until consent is obtained, depending on their particular circumstances.

WHAT APPS ARE ALLEGEDLY SENDING FACEBOOK DATA OF NON-USERS? This flaw was first pointed out by Privacy International in December when an investigation found 23 popular apps all did the same thing. Users log in and information is automatically sent to Facebook before a user can give, or not give, their consent. All the apps tested by London-based charity Privacy International have millions of installs. They are: Yelp

Indeed

Duolingo

King James Bible

Qibla Connect

Muslim pro Advertisement

'We also require developers to ensure they have an appropriate legal basis to collect and process users' information.

'Finally, we provide guidance to developers on how to comply with our requirements in this regard.'

Under GDPR legislation, the legal obligation for processing third party app user information lies with the app developers.

The charity argues that the types of app and how often they are opened, which is all that is transmitted, can be used to paint a 'fine-grained picture of someone's interests, identities and daily routines'.

Privacy International has said it is urging the apps to fix this issue and also encouraging Facebook to change the default setting so this doesn't occur.

Language-learning app Duolingo says it will be issue a software update it its next release on both Android and iOS to remove the Facebook SDK App Events component.

'Duolingo thanks Privacy International for their important work raising awareness of this issue,' a Duolingo spokesperson told Cnet.

'As part of our ongoing commitment to privacy, we are removing the Facebook SDK App Events component from both the Android and iOS apps in the next version releases.'

Yelp claims the allegations levied against it are unfounded.

Zuckerberg is now promising to apply the same privacy principles it used in WhatsApp to all of its services moving forward. File photo

A spokesperson told MailOnline that its Android app 'does not also send personal data to Facebook at launch.'

'Yelp runs ad campaigns for its apps on Facebook. To do this, when launched Yelp's Android app may transmit a device's anonymous advertising ID to Facebook.

'This use is described in Yelp's Privacy Policy and Android users can, at any time, choose to deny access to the advertising ID through Android settings.

'Contrary to this report, Yelp's Android app does not also send personal data to Facebook at launch.'

This is the latest scandal for Facebook in a string of privacy concerns.

Mark Zuckerberg announced just yesterday the company's intention to bring end-to-end encryption to Messenger, WhatsApp, and Instagram messaging services.

This, it says, is a the first step in Facebook shifting toward a 'privacy-focused' future.

The Facebook boss acknowledged the site's reputation, which has been tarnished in recent years as a result of its lax-approach to the protection of its users' information, and promised to rebuild its services on the principle of privacy.

Zuckerberg also said he's working to ensure your online activity won't come back to haunt you later in life.

Ultimately, the CEO says the firm is striving to make interactions across Facebook 'a fundamentally more private experience.'