Website attacked by unauthorised adverts, please help!

Hello,
Recently my website has been attacked by unauthorised adverts. They appear at the top of a post, not within the boxes. Here’s a post with one in:

http://www.literateur.com/days-of-roses-ed-declan-ryan-and-malene-engelund/

It appears on the post as the following at the bottom of the entry:

[Code moderated as per the Forum Rules. Please use the pastebin]

There are two blocks of these things. On one level it’s quite easy to get rid of in that if I delete this from the post, the adverts disappear. However after a while it keeps coming back and it’s all over the posts on the site. Please can someone help in getting rid of these? I’m pretty desperate.

Thank you in advance,

Best,
Kit