I haven't experienced any particular problems like this, however, once someone has logged in they can send you emails via the forum. You can change  the option in your forum Privacy settings  so that emails can't be sent that way. From the amount of junk appearing it looks like we have no defences in place, but this is far from the case and only a small percentage actually gets through. Initialy software is used which blocks bots and other malicious software from even getting to the site. This has blocked around 2500 attempts in just the last 7 days. Next there si software which filters out junk. This is detecting and rejecting  around 20 posts a day.  I do a quick check to make sure no legitimate messages are being rejected, but this rarely happens. In addition users have to be registered before they can post to the sites. This includes a litlle test to prove that they are human. They need to provide an email address and need to have the password emailed to them. This stops attempts to register  invalid email addresses. We can't stops users who go through these processes from registering, and  I understand that some of the advertising spam is coming from individuals being paid a few pence a time to join forums etc. and to post advertising material. Some is also from people with nothing better to do, hence the big increase over the weekends. Finally,  as soon as any of the forum administrators see any spam they delete the users  and  all their post.  If it is done quickly enough it stops the posts appearing in the digests etc.  If it looks like we are getting regular spam from the same source then the ip adress is also banned. Anyone regsistering but not posting a message is deleted ina regular tidy up.