This depends on their data use and privacy policies. Thankfully, many companies are starting to realize they need to become more transparent.
Up until now, users of the biggest social networks have been expected to read thousands of words to understand how their data is used. And, let’s all be honest now, we don’t always read the terms and conditions we agree to.
For example, if you request to download all of the data that Facebook has on you, it’s likely to include your entire history of messages, and a full list of your mobile phone contacts. The items that come up prominently in your News Feed are often based on the things you have liked and commented on in the past.
Staying logged into a social network can mean it can see practically all of the other sites you visit and this information is sometimes used to serve up adverts you might be interested in. Some companies also aggregate your data so advertisers can reach very specific demographics, such as a 30-something male, living in New York, who owns a dog and likes burgers.
Public awareness about the use of private data by social networks has been heightened by the recent scandal engulfing Facebook. Cambridge Analytica, a data analytics company, allegedly harvested personal data from at least 50 mln Facebook profiles without consent developing an algorithm that targeted voters during the US election.