If Facebook's legal team wasn't already on high alert, it certainly is today as the social network is being sued by three Facebook Messenger users for violation of their privacy. The alarm bells will be ringing at Facebook because the lawsuit seeks class action status on behalf of all affected users as well as asking for unspecified damages.

As Reuters reports, the lawsuit is in response to the revelation earlier this week that Facebook has been logging call and SMS data from Android users for years. Facebook admits collecting the data, but flatly denies doing so without permission. As far as the company is concerned, we gave it permission to collect this data.

It's the permission aspect that has been called into question by some users who believe they never did give permission. Alternatively, the opt-in to data collection may not have been very clear or set as a default response in certain cases.

This lawsuit, if it goes ahead, will need to identify what happened in all cases. That may prove difficult due to the frequency with which mobile apps get updated, but the focus will be on Facebook to produce the evidence to back its claim permission was always clearly requested before data collection began.

Facebook's worst case scenario involves the lawsuit being granted class action status and fault found in its process of asking for permission. That would open the company up to having to pay damages to what could be tens of millions of Android users who used Facebook Messenger over the past few years.