Anna
Thanks for the info - I spotted one "odd" post earlier which you have now removed.
Just a point. Most spam is automated. It is the only way the spammers can get the volume of posts that suits their percentage game. i.e. that two in a thousand people might be duped into responding.
So they are constantly trying to circumnavigate the security on whole servers/databases etc. etc.
You may have seen that a number of websites/forums are now adopting the CAPTCHA protocol.
http://en.wikipedia.org/wiki/CAPTCHAAnother pain for genuine users - but if the problem persists may be the only way to go.
Just a thought.
MB