With so many people now working from home, video conferencing service Zoom has become a household name virtually overnight. But while millions of users appreciate the ability to connect with the office, colleagues, friends and family for free, a worrying privacy issue has been found.

The Zoom iOS app has been spotted sharing data with Facebook... even for users that don't have a Facebook account. So what's going on?

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Zoom's strange activity was first reported by Motherboard's Vice, where Joseph Cox says the fact the app includes the Facebook SDK is to blame. It doesn't matter whether you have a Facebook account or not; Facebook users and non-users are treated in the same way. What's particularly disturbing is that Zoom's privacy policy makes no reference to this data sharing, so iOS users are (or at least were) completely ignorant of what has been happening in the background.

What is Zoom sharing with Facebook? A surprising amount of data, it turns out. Network analysis show that the app connects to Facebook's Graph API and tells Facebook when the app is opened, details about the device being used, what time zone the user is in, what city they are in, the phone carrier that's being used and -- worryingly -- a unique advertising identifier.

In a message to Vice, iOS researcher and founder of privacy-focused iOS app Guardian Will Strafach reacted to the findings by saying:

I think users can ultimately decide how they feel about Zoom and other apps sending beacons to Facebook, even if there is no direct evidence of sensitive data being shared in current versions.

Facebook's policy relating to the use of its SDK and tracking pixels specifies that people must be made aware of the fact that data is being shared with third parties, including Facebook. It also specifies that users should be given the opportunity to opt out of tracking. Zoom does not comply with either of these requirements.

So far Zoom has not responded to requests for comment.

Image credit: Konstantin Savusia / Shutterstock