It may not be related to your WordPress install directly, it could be coming from another user’s site on that server, typical shared hosting accounts are not very secure.
The best thing to do for the security of your site would be to move it to a more secure server. I do offer Super Secure Hosting for $12/month per site. If you just have this one site to worry about then you should just move the site to my server and be done with this. I have moved hundreds of infected sites to my servers and non of them have ever been reinfected again since.
I got your other direct email so if you are interested in hosting with my you can send me your hosting details directly to my email and I can move the site for you.