On 6/18/2018 users of flightradar24.com received an email informing them that their data may be at risk due to databases being compromised. The email reads the following
Dear Flightradar24 user,
I regret to inform you that late last week we identified a security breach that may have compromised the email addresses and hashed passwords (see explanation below) for a small subset of Flightradar24 users (those who registered prior to March 16, 2016), including you.
By the wording of the email it seems that an old database was compromised. More information is still to come as users continue to ask questions.