No web server is entirely secure.
In fact, there are armies of individuals out there whop delight in penetrating web hosts and ISPs web servers and defacing sites or stealing ontent.
They do it for a number of reasons, often purely so that they can say to their friends 'Look at my latest...'
Without access to the account nobondu will be able to tell you anything at all and even with account access there will probably be little to learn.
The staff at Easily should be able to offer more details, but I'd be unimpressed at anyone gaining root access to my web site and molesting its contents.
I suggest you press them for rapid action and insist that your account and the server it is on is locked down at the least. I would also suggest your username/password combination is renewed - in fact, asking them to create a brand new account for you is not too unreasonable, possibly even asking them to shift you to another server in the process.
No ISP or host can guarantee web server security 100% and I think you'll find that this is far worse from Easily's perspective than yours. If this is not isolated and I'd imagine it isn't, they could well have a very serious problem on their hands.
My last point: grab a last backup of your 'thousands of pages' if you haven't already.
Network and server security is no small topic and there could be any one of dozens of ways into a web server. Most commonly used methods are relatvely easy to guard against but others are not.