What is a Windows hidden share? And what is it good for?
Does removing Windows server default hidden shares impact the system?
Simply a share that isn't displayed by normal means in the network. Other users will not see your shared folder/files. Certainly it is not a means to secure shares from others, since many networking tools can still find these shares. Hidden shares have the exact same security characteristics of normal shares, though. So you can still create permissions and require passwords to access them.
Hidden shares may be useful if you want to share a file or folder to someone and don't want it listed on everyone else's computer. They are particularly useful to programs that require shares to be function (like some server software, or some specialized software like Virtual Machines), since any number of shares can be created without clogging the list of shares your computer publicly advertises on the network.
Not normally. Not unless your computer is on a network. Certain administrative functions also make use of these "default" shares (called Administrative Shares). But to my knowledge, always in the context of networking. So I would say, if you are not in a network, it's safe to disable these shares.
Note that these shares are secured with your computer administrator credentials. So they are very safe unless someone knows your administrator account. But, if they do, a lot more than your administrative shares will be compromised :)
This technet article explains how to make your own windows hidden shares, and gives you some information about them.
From the article:
Removing the drive letter shares will prevent administrators from having remote file system access. If you really need that level of security on your system, you might want to just disable the server service.
They are exactly that. Just shares. I wouldn't worry. Share permissions are weak. NTFS permissions(those that are stored on your disk) supercede share permissions.
If a service decides to wander into the share permission, they'll just get denied at the disk because of NTFS. Share and their permissions are left in for backwards compatibility.