As Randy, us, and others mentioned several times through these conversations, spam is a walk of life on the internet and odds are you will never be able to 100% combat it. It also comes in cycles. Points that are high, turn to lows as people adapt spam measures and combat spam accounts or our spam defense grows aware of individuals, etc... However, our methods posted here will make it significantly less annoying and to a degree remove it from being a daily hassle.
As Randy mentioned, we take significant measures with each release to ensure that we release the best software possible to our customers. We have mentioned several times in this topic that we're happy to look at what you're seeing but we have not gotten a specific example. We have, however, looked at a recent example of a banned member and they have compromised email/password combinations from other websites around the web (non-IPS) so that would explain how a malicious-intended spammer could gain access directly, with no brute force. If this is not an active member, banning them, as you've done, is the right measure. If it is an active member, you may wish to change their password and contact them. However, it could be that the spammer/attacker has access to their email inbox so be mindful of that.
If you would like us to take another look at another example or have a further complex example than just a username, please feel free to us the Contact Us form at the bottom of each page and we'll be happy to take a look.