I cant figure out but thats a possible a hack attempt. Thank god that you haven't installed plugin named tiny_mce
I hope that im wrong....but you are in big trouble!
Try to see your page source,look for links that should not be there.
After i have post that here....nothing happened.And 3 or 4 days ago i have notice something funny about my blog.
In the source of web page,i have found one link pointing to some dating site,Turkish.

As my site is about different think,this became suspicious.
After that i have dig in my blog and found that all .php,.css, files was infected.
Also the virus create entry in database,
rss_29138649827634912873649,something like this.The hack can be seen only by search engine.Normal visitors cannot see anything.Or the person who manage the site.
In the last 2 days i have recovered about 90% of the site.Fresh install,new database,new template....
Nobody knows how the virus get in the site.Are some queses that might be supercache plugin,or the rss feed,wp team works on that.
But the problem is that if in that account have more than one blog,all get the virus.Same to me,it was 5 blogs on that account,all got the virus.
I have saved the hacked versions and i will take a look on them later.
Update: Not sure,but if you have this entry,your are hacked: jquery.js
search all files in all folders,also hidden one,search with ftp,ftpzilla,or what you use.
I have got that entry,and was hidden.Some claims that is created by the virus.
What people know so far,the malicious code,is in the database,and the codes from .php trigger it.
For futures info:
google for pharma hack for wordpress.But this one is different,nothing about pharma,and does not redirect your visitors,or add any link to your serp.Just create backlink to his site.
I have no idea how long that code was there....
Also if you just try to disinfect,even if you delete WP,and make clean install,with same database,reactivate after 20 days.
I use to have wp 2.9.2,all plugins up to date.....
If anyone have this,i can give a hand how to restore.But,all files must be deleted,including database.
Update:Look for this entry,in all folders and subfolders:jquery.js
Some claim that is create by the virus.
I have found that,on my blogs,was hidden.Make sure you look for it with ftp,i have useed ftpzilla.In cpanell didnt show.