This might be a good time to upgrade your wordpress setup since Lorelle.Wordpress.Com reported that this attack impacts ALL versions of WordPress up to 2.8.4.
It is reported that if your permalinks have been changed to something that looks like example.com/category/post-title/%&(%7B$%7Beval(base64_decode($_SERVER%5BHTTP_REFERER%5D))%7D%7D|.+)&%/. The keywords are “eval” and “base64_decode.” Then you probably have been hacked and should upgrade immediately.
Usually upgrading Wordpress is fairly simple. You will get a notice for upgrade, just click that link, upgrade your files and nothing major should be affected within your blog.