which type of server do u find safe --- Shared or dedicated server?
And how to know that my server is hacker-proof?

Shared server are those on which differnt sites are hosted on the same server but in dedicated server the server is dedicated to only one site.. It lots depends on the web hosting company that what kind of hardware and software they use. Shared hosting is even safe but the problem with it is that its has to cope with lots os different sites with diffrent types of visitors so it tends to get slower , but this is not so in Dedicated server..

dedicated are surely more safe

How are dedicated servers surely more safe?

It depends on the host and who is setting up the server. You can have the safest experience based on shared or dedicated based on the level of management and experience of the company or person who is running it.

In some case a shared server is so well tweaks and is checked on so often, yeah, it can be safer.

But what is your definition of safe?

WEBster Computing Service - webcs.com
dedicated server hosting / shared hosting
One of the oldest hosts on the planet