In terms of security, only a few folders are accessible with password-less file sharing, and although anybody with access to the network can access them, the damage an intruder can do is limited to stealing or modifying just the files in a few folders that are known to be public.
Passwordless file sharing has two disadvantages: First, and most important, it is crucial that you have a firewall in place. Otherwise, everyone on the Internet will have the same rights in your shared folders as you. (That’s one of the reasons for Windows Firewall and why Vista is so adamant about either installing the Firewall or disabling file sharing.)
The second disadvantage, although less troublesome and probably less noticeable to most people, is that if you attempt to use a shared folder from another computer on which you have the same username and password, you won’t get the full rights that you’d have locally. You’ll be a guest, like anyone else. In particular, the very handy whole-drive administrative shares such as C$ do not work when password-less file sharing is in use.
The second file sharing option in Vista is Password Protected File Sharing. By default, Vista uses password-protected file sharing, which is much more secure because it limits access to the Public folder and all other shared folders to users with a user account and password on your computer. Password Protected File Sharing provides for finer granularity of control because you can set sharing permissions for individuals and groups. You can also give individuals different permissions, depending on the type of access they need.
Knowing the disadvantages, if you want to make the Public folder accessible to everyone on your network, you can disable password-protected file sharing. Click Start, Control Panel, Network and Internet, Network and Sharing Center. Under Sharing and Discovery, click the drop-down arrow beside Password Protected Sharing, click Turn Off Password Protected Sharing, and click Apply.