Spam operators using bots to promote adult-themed services change their tactics to avoid Instagram’s detection mechanism. Redirects remain the main stratagem but they come with other tricks meant to push the user towards a particular website. These accounts give little to Instagram’s protection mechanism to pick on. These type of accounts are intermediary, in that they do not provide visitors a link to the source of the adult content. The operator behind this campaign has been active since at least the middle of 2016 and created almost 1,500 accounts.
Source: https://www.bleepingcomputer.com/news/security/porn-bots-on-instagram-switch-to-more-guileful-tactics/