what about to use a captcha system for the borad?
I'm not conviced captchas work, when I added them to my own site it barely slowed them down.
The attacks Arduino.cc's has been suffering, are Bot attacks, and bots "cannot" navigate sites protected by "good" implementations of CAPTCHAs, such as the format used over at Yahoo.
The general mentality of spammers is if they can let their bot's roam the web injecting their filth into millions of vulnerable forums, like this one, then it beats doing any form of work themselves, like reading site CAPTACHA codes for a single attack, especially if the pay-off isn't high unlike the persistent attacks suffered by WindowsLive and Gmail whose CAPTCHAs were hacked, which considering the "kudos" prize, its no wonder.
So for the 5 minutes the Yabb hack takes to implement it'll reduce a substantial amount of the misery users here are obviously suffering as a result of sometimes highly offensive spam.