Process started from system command in C inherits parent fd's

I have a sample application of a SIP server listening on both tcp and udp ports 5060. At some point in the code, I do a system("pppd file /etc/ppp/myoptions &");

After this if I do a netstat -apn, It shows me that ports 5060 are also opened for pppd! Is there any method to avoid this? Is this standard behaviour of the system function in Linux?

Thanks, Elison