Application is already precompiled

Today I had an error message “application is already precompiled” on my website.

The site had been up and running for over a year, and suddenly it stop working. When I copied the website back to my computer and rebuild it, the error message appeared.

There were several problems to this. First one was that it had an added file called PrecompileApp.config, second problem was in two or three of the .aspx pages in the inherit tag there was a reference to a dll file called App_Web_6ecyhum5 . The third problem was in the bin folder, a dll file with the same name App_Web_6ecyhum5.dll existed.

I have no idea how these could be added automatically unless someone hacked in and added them manually.

Also, three or four reference of the CodeFile was deleted.

To fix all the errors, I deleted the PrecompileApp.config, App_Web_6ecyhum5, App_Web_6ecyhum5.dll and added all the references back to the CodeFile.

The site is very simple with an email form and the rest being static pages with flash header on each page. No magic here.

What could have caused this?