Re: What do your spam signups look like?
Same problem,started about a few days ago. Bots are signing up a few times a day, firstnamelastname19xx.
Interesting is that I notice in my stats some ip found my site by searching for “proudly powered by WordPress MU and BuddyPress”.That could be a reason that this particular bot is finding and attacking bussypress installs.
If this bot is getting past Captcha, I would recommend applying a reverse Captcha technique. Just do a bit of Googling on this, it uses a hidden field as a honey pot which bots will fill in, but normal users will not. When filled in you can redirect them to a page of your choosing.
Please report your findings and how you deal with this as it would be very helpful.