It does look like your host does use IIS. Just typing in the URL with a
random page name afterwards is enough to tell you. The page returns:
HTTP 404 - File not found
Internet Information Services
That would bring up this question- is your site hosted and administered somewhere where you control the server, or are you paying a hosting company for webspace. If the former, a number of people in this thread have already indicated they would be happy to help you out in securing the server. If the later, I suggest you contact your host about the incident, and ask what methods they have in place to secure their servers.