@Freya , I hear that these zombie spam bots are at it again but this time it's been ramped up with links to explicit and illegal sites.....
As a suggestion, how about locking down those affected accounts? Place them on read only until until the member gets round to changing their password. Inbox them (the member) about this and as an extra blanket of security, have staff screen posts for a set period of time until it feels it's ok to lift restrictions.