Credential-stealing malware targeting premium accounts on adult websites almost tripled in 2018. The malware is typically some kind of repurposed banking trojan; the bad code redirects victims internet traffic to fake webpages that mirror an authentic adult site they are attempting to visit. In 2018, Kaspersky Lab experts found around 10,000 unique offers for premium-access credentials to porn websites. Cybercriminals that buy the credentials can monetize these in many ways, including taking the stolen access to pornographic websites and reselling it at a cheaper price than the cost of a direct subscription.
Source: https://threatpost.com/porn-malware-dark-web/142105/