Page Temporarily Unavailable

Hi,
Sometimes I get an error when trying to acess my wordpress backend and foreend (no matter what page), and then the error disappears sometime later, and I can access my blog again. The error is “Page temporarily unavailable. Please try again later.” This happened for me once, I read that it was malware, and I deleted everything and started over, since I was only building my site. The second time it happened, and when I was looking through my files, I found a folder among the plugins that did not belong there. I deleted everything, changed all my passwords, and reinstalled wordpress. But before I have had time to reinstall all plugins, build the site, etc., the error is back for the third time.
I know I have not shared my passwords with anyone (unless someone stole them), I have according to advise moved my wp-config.php to the root directory, and all permissions for folders are 750 and for files 644.
Now my questions are: Is it really malware/hacking that is the problem? What more can I do to prevent this from happening?
I am using freehosting.com for my hosting, and I am wondering whether that is where the malware (if it is malware) comes from. They do not say whether it is shared hosting.
I would really appreciate some specific help, as this is confusing and frustrating, and I do not want to pass on malware (if it is malware) to my visitors. If it is the hosting, what shoud I use that is not too expensive (I am using freehosting because I cannot pay a lot for hosting)? Just please don’t tell me to use wordpress.com, as I have looked at that and it is not something for me. I want to learn this www.ads-software.com stuff! Thanks for all help.
Sincerely, Maria
Blog: creativevegancooking.com