Hi,
On
http://forum.openscad.org/ a few weeks ago we got a spate of SPAM.
It was from Registered Users, mostly with obviously computer generated usernames & emails on gmail.com
I changed from Registering only for new posting & replies to Membership required.
I did a bit of digging and got a link to
https://github.com/ip6li/TrashmailIt appears to be a system to automate the registration emails.
While I have no proof, I suspect a Spammer may have been able to automatically process the registrations.
This requires the captcha to be completed, hence I suspect the, fairly simple, captcha used here may have been breached.