I had several accounts sign up for my site and send thousands of PM messages across my site to all sorts of members

The messages had a link to a spam site.
It was the kind of link where once you click it all kinds of stuff starts popping up and the user can't click out.

My members are quite upset.

Any good ideas for preventing this?

Set messenger restrictions for the default member group?

Mine aren't allowed to send more than one message per 30minutes with a maximum of 2 recipients; They're also completely barred from our chat system.  After they reach 5 approved content, they're moved to the regular member group automatically and these restrictions are lifted.  Most members who use the site legitimately don't realize these restrictions are in place and only effect those who are there to spam. These restrictions, along with completely disabling the useless Contact Us form, has drastically reduced spam on our site from a several times daily occurrence to occasionally per month via a rogue topic or two.

1 hour ago, Alismora said:

along with completely disabling the useless Contact Us form

"Contact Us" isn't useless to me. It's the only way new members can join my site. Registration is disabled until a prosective member writes me via the Contact Us form. 

That's.. nice? They wanted advice on preventing spam, and I obliged using the knowledge I have with my own community that may work for them as well.  Your experience doesn't negate mine, and I wasn't initiating a debate on why it's useless for my website.  🙂

3 minutes ago, Alismora said:

That's nice, but your experience doesn't negate mine.  They wanted advice on preventing spam, I wasn't initiating a debate on why my website thinks its useless.  🙂

But you felt a need to say it was useless. I was merely disagreeing with you whether you wanted a debate about what you said...or not. ;) :D

2 irrelevant posts in the same topic.  😨

Good luck with whatever methods you choose @SJ77.  🤞

On 6/14/2019 at 7:25 PM, SJ77 said:

I had several accounts sign up for my site and send thousands of PM messages across my site to all sorts of members

The messages had a link to a spam site.
It was the kind of link where once you click it all kinds of stuff starts popping up and the user can't click out.

My members are quite upset.

Any good ideas for preventing this?

2 things. If you can use "Flag as Spammer" and enable that to delete all of that member's content, it should delete the PMs as well. Have mods use it if they get more of those reports. Also set a new members group that has limited or no PM functions until X items of content are approved (I don't know your community or how large it is, etc. Set X to something that's decent for what a newer member would be posting.) This should keep you relatively safe from this, and allow moderators and administrators to respond faster to reports.

3 hours ago, AlexWright said:

2 things. If you can use "Flag as Spammer" and enable that to delete all of that member's content, it should delete the PMs as well. Have mods use it if they get more of those reports. Also set a new members group that has limited or no PM functions until X items of content are approved (I don't know your community or how large it is, etc. Set X to something that's decent for what a newer member would be posting.) This should keep you relatively safe from this, and allow moderators and administrators to respond faster to reports.

turns out it doesn't delete the personal messages they have sent 😞

1000's of spam personal messages sent and no easy way to remove them.

We only allow to send PM after 5 post. That solves the issue for us. Before 5 post if anyone needs help, contact us is only option.  For contact us  - we use @Adriano Faria addon which has much better options over contact us. This way any active staff can see and help. 

PS Good luck combating spam! Never ending issue :(