|Uh.. now I know what you meant. |
If they knew your IP address and your comp. password, they
can access it via RDP or Administrative Sharing (like C$,
Admin$, D$ and so on). Otherwise, they probably use Packet
Sniffing technique to see your network / internet activity.
RDP and File Sharing by default, included in Firewall 'allow-
If otherwise you've installed / setting-up a Personal Web
Server on your comp., it's a whole different story ;P