Every wiki has had at least one spam attack. We, unfortunately, have had more than one attack. At least every season, we have a spam attack, like the [blocked due to spam filter] incident (ask around if you weren't here when that happened). Recently, 2 users (their usernames were inappropriate, so I won't repeat them here) attacked pages by leaving explicit messages on the pages.
Unfortunately, there's no way to permanently ban spammers/vandals. There's no "all spammers immediately blocked" option for the wiki. It would be cool if we did have one...in fact, it would be really helpful...but I don't think tech is advanced enough for that to happen.
If a spammer or a vandal (I'm beginning to wonder if there's a difference...mainly because I don't feel like saying both, because then this blog would be unnecessarily long) comes on, they are often very persistent. You can undo their edits, and they'll just keep coming back.
The best protocol for stopping this (I was watching Star Trek today, and they said that word a lot) is to revert their edits, and report the problem to the administrator's noticeboard. If they're persistent, just keep reverting their edits until an admin can stop them.
Now for some good news
Once a vandal (that's the word I've decided on) leaves vandalism, he or she (I'm not gonna go through a whole thought argument on that topic) thinks that the vandalism will stay there. But it won't. Because it's guys like you and me (thank you 7th Grade English) that can prevent their vandalism from disrupting the wiki community. And it's a relief to know that once a vandal is blocked, he (or she) stays blocked. And if the vandal (I'm not gonna say "he or she" again) comes back using a new username, it'll (because I've decided it's an "it") be blocked again, and again. Because the users on this wiki are on a staircase, defeating a continuing problem one step at a time.