From The Verge:
However, there are obstacles for Spotify to dodge as it continues to grow. Recently, it had to crack down on users running modded versions of the app to stream music for free while blocking ads. Spotify’s IPO filing notes that about 2 million users are getting around ads on Spotify without paying, or about 2.3 percent of all free Spotify accounts.
It’s not good enough to not pay a monthly fee but these leeches don’t even want to listen to the occasional ad to which pays for the service they’re using.