Spammers started using vbulletin to send spam emails last night -
not to oople users, but using vbulletin to access the mail system on the server to send random spam to a list of random addresses. I got loads of bounces so that's how I knew.
Tried everything to find the weakness but in the end had to turn the vbulletin emails off for a lot of stuff - I checked and people can still sign up but let me know if you notice any functionality missing and I can decide what to do.
Obviously this is a quick fix to solve the issue until I find the reason it's happened - but it's annoying to spend hours on something like this