To transfer data packets between two or more networks, a is used.

To transfer data packets between two or more networks, a router is used. The router is a networking device that works on the OSI Layer 3 and is able to transfer and forward data packets between several networks. The router is capable of reading and using the source and destination IP address of the data packet, which defines the sender and the receiver of the packet. 

Malware, not sure what else would fit that description.