Question: Windows (in this case XP) allows me to simply "share a folder" via its [SMB protocol](http://en.wikipedia.org/wiki/Server_Message_Block), and I can access it via Linux quite nicely (with [Samba](http://www.samba.org/)), no questions asked.

That's what bothers me, it just does not feel secure, and the ["security" section](http://en.wikipedia.org/wiki/Server_Message_Block#Security) of the Wikipedia page is discouraging.
I love being able to just tell Windows to share a folder and imediately have these personal files on the Linux box (and with R/W access), but I don't want these files to be deletable or even accessible from the internet. I'm not even being asked a password! Can people all over the world access my shared folders without a password too?

The topography is: One machine Windows XP SP3, the other Linux Mint Debian edition, and both connected to the internet (and to each other) via a router that my ISP gave me. It has WPA-encrypted Wi-FI, but I connect these two via LAN cable.

Am I secure in my usage of Windows' file sharing (maybe by being behind a router)? Do I have to do something?

Answer: 
A properly configured router with a built in firewall and network address translation (NAT) should give reasonable protection.

There are many websites that will perform a port scan and tell you what file-sharing and other services are visible through your router. For example "Shields Up" at www.grc.com.

![Shields-Up! report](https://i.stack.imgur.com/xaQv3.png)

*Other such services exist, you can also do it yourself using a port scanner such as nmap*

It is good practice to use user-ids and passwords to protect your file shares. Windows allows you to choose the level of security. Samba on Linux can work with at least some types of Windows file-sharing security (it's a while since I used it).
A work around I use is to put a 3rd party firewall on XP (disable XP firewall), set a rule to only allow the ip address of your other PCs to be able to connect to the XP box, I use the old Sygate firewall for this on all my XP boxes. Sygate is no longer supported but works flawlessly for me.

Once installed you can allow or deny outbound using the popups when the show, and to set inbound for your network adapters go to Tools >Options> Network Neighborhood Tab in the sygate interface to configure inbound protection, Untick "Allow others to share my files and printers", do this for all network adapters you have using the drop down box to change adapters, then hit ok. Now go to Tools>Advanced Rules to allow the IPs and protocols/ports you need using the "add" button. 
[I use Sygate free version 5.6.2808](http://www.oldversion.com/Sygate-Personal-Firewall.html)

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![enter image description here](https://i.stack.imgur.com/VKu0o.png)

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![enter image description here](https://i.stack.imgur.com/lwXZw.png)

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![enter image description here](https://i.stack.imgur.com/BOZpX.png)