you have to enable security protocols,there are many like WAP(old one) WPA,WPA2...
latest is WPA2.
so
login to your office wireless router and enable WPA2(wireless protected access V2) protection.check your router settings..
almost all wireless router supports this.don't know which one you are using!.
here is a setup for belkin wireless router
more info
*www.computerworld.com/s/article/9002706/Tutorial_How_to_set_up_WPA2_on_your_wireless_network_