The security blog of Opera browser has an interesting short write-up about a security breach that happened to them:
Earlier this week, we detected signs of an attack where access was gained to the Opera sync system. This attack was quickly blocked. Our investigations are ongoing, but we believe some data, including some of our sync users' passwords and account information, such as login names, may have been compromised.
[...] The total active number of users of Opera sync in the last month is 1.7 million, less than 0.5% of the total Opera user base of 350 million people.
(Score: 2) by Celestial on Sunday August 28 2016, @11:33PM
If it takes into account the multiple installations of Android and iOS versions, that may help explain the figure. It makes for a decent Android browser, with the built-in ad blocking.