Use a plugin like Akismet, which takes out 95% of spam posts instantly for most people. If that doesn't help, you can disable comments on that post specifically by going to your Manage --> Posts --> Specific Post --> Options section.
As the two above me have already said, disable comments for that post. Manage- Post- Specific Post-Advanced Options-Comments and Pings-Uncheck the Allow comments box.
they might be bots. I use wp-recaptcha plugin. the user has to enter captcha when they want to add comments. This will save avoid at least 95% spam comments. I used to get around 100 spam comments everyday. after installing this plugin i am getting around 5 to 10 only. I am still not sure how this 5 or 10 comments are getting into ??? are they entering captchas or do they by pass this captcha ?? I have no idea. but this plugin does good job. however, there may be some impact on normal users. some people don't like to enter captcha to add their comment on our site.
good advice dpsubi1 Akismet + ReCaptcha = SPAMPWN There are advanced spam servers that use CaptchaKiller to bypass the captchas, even the most complicated ones.
I use a combination of BadBehavior and Akismet on my blog and i've been 100% spam-free for quite a while.. on my big site i use a combo of BadBehavior and Mollom.. it's 99.99% spam free..