I went to http://www.wincert.net/forum/files/ and used the "Download" button, which links to a file "WinToolkit_220.127.116.11.7z", with a size of 10.256.282 bytes, containing a file named WinToolkit.exe. When I try to go to any of the links in the "Downloads" menu of the program, i. e. the pages to download the Windows ISO files, the browser tries to open a page which most propably just contains ads (URL looks like adf.ly or something alike, I closed it immediately) instead to the Microsoft page with the ISO file(s). The same happens when I try to go to the Firefox download page.
Somehow someone stupid but greedy (does (s)he think this will not be noticed?) must have been able to replace the 7z-file on your server or something else.