Spotify is taking action against “pirates” who are accessing premium account features without paying for them. This requires a hacked version of the mobile app; which is all that readily available and isn’t exactly widespread.
The music streaming service has been sending emails to those suspected of using the hacked apps; saying that “abnormal activity” has been detected on their accounts. The notice also warns that continued detection of the activity could result in the account being suspending or terminated.
What appears to be happening is that people are using hacked versions of the Spotify mobile app; which allows them to circumvent the minor inconveniences that are associated with using a free account. These are things like being subjected to advertisements and limitation on skipping songs. Most of which are designed to encourage people to make the leap to a paid premium subscription.
This action is unlikely to actually have any impact on the number of hacked accounts. Seeing that there is nothing stopping these people from simply opening a new one using a different email address.