I am hosting a web space with one company and couple days ago i noticed that all my data have been lost and webpage was set for default. When i contacted the company (Nevidia) they told me they do not know how information disappeared and they could not restore it. I have a lot of sensitive information on the server.
If you believe that your web site was actually compromised somehow, as in by a hacker or someone who maliciously stole your sensitive info, I would bring that concern up to the web host. Ask them what logs they might have to help investigate that possibility, and try to make sure it wasn't a problem with their server security. Also, you should probably consider any programs or design features you had on the site that may have security issues as well.
If the data really is important and you intend to post it again, you should figure out the source of the problem and prevent it happening again first.
You should NEVER EVER EVER host sensitive data on a shared server. If you have data that is important enough that it will be a problem if its compromised, you need to get a dedicated server and shut off every feature that you're not actively using.
As for lost data - always keep backups.
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Contact the host for the logs. They should be able to tell you whether or not the server was compromised or give you an idea of what happened. Give them some time, and if they still say they don't know, it's time to find a new host. I hope you have backups, otherwise count this as a lesson learned.