TS, you are not that smart either.
Steal wifi just for downloading purpose? lol

There are lots more things you can do when you connected to the same
network
1) Configure honeypot to capture encrypted pages, bank accounts, facebook, etc.
2) DOS attack
3) Packet sniffings - email accounts, ym chat, etc
4) File sharing
5) Keylogger client deployment tools

Less than 0.0001% Malaysian knows how to do that..dont worry
Imagine they don't even know how to configure client DNS..lol

Blocking MAC address only makes abit tougher and longer time.
1) For a patient hacker, he just need to monitor the SSID , and clients associated with it.
2) Copy all the MAC address of the legitimate clients connected.
3) Wait for one of the legitimate client to disconnect from the SSID.
4) Spoof your own MAC address to the legitimate MAC address.
5) Then you begin cracking the key.

Most secured method for WIFI - impossible to hack :
1) WPA 802.1x + RADIUS authentication server
2) IPSec - for IP authentication & encryption .

Are you sure you want to do that? Let me share with you something.

1) When you browse the Internet or download/upload etc , your IP = public IP
Example: www.whatip.com , you able to see your own public IP.

2) Your pc is behind Network Address Translation(NAT) , which config. at router, your pc IP = internal IP
Example: 192.168.1.2 , which assigned by DHCP and is not routable. Check at command prompt: ipconfig

3) Someone connect to your network, which also assigned by DHCP , example: 192.168.1.3

4) When "someone(192.168.1.3)" download illegals stuff, the web will see the IP as public IP . What you can track is just
time, hostname and MAC address, which no value if being spoof.

5) Therefore, if you report , most probably will track to your account , because the public IP is registered under yours.