Is there anything on your system which you use an API or otherwise to post on your community? That would be a way around it as it isn't going directly through our software.
Our Spam Defense tool works on spammers, not their content. The idea is to stop them at registration, not when they are posting. One spammer could have 50 clients and could have several variants to post so stopping one message would just lead to them posting another but flagging the user as a spammer will then send this back to our system where if enough individuals do or we see a trend on our numerous points at registration, they will not be able to register on our clients' communities.
The system is not 100% perfect though and this is due to the nature of spamming and the internet. There are bot and human spammers. It is as profitable for them to figure out our systems as it is profitable for you and us to prevent them. Spamming goes in phases as well, we always see an uptick around the holidays and new year (you can imagine why). The more you report to the system, the more it learns.
If you haven't already, I would also recommend reviewing the Question And Answers feature for Spam Prevention in ACP -> Members -> Spam Prevention. A good Q&A question on registration is one that is immediately known by your audience but is hard to Google. It takes some time to come up with one but you will see a drastic decrease in spammers registering with the right questions. You also want to rotate these questions in and out, don't leave them up for a long period because as I said, there are human spammers whose sole jobs are to figure these out and post them on a huge spammers database once they do.
With all that said, if you have any suggestions for the Spam Defense system, please post these in our Feature Suggestion forum for further evaluation.