MK0-201 Question #220: Real Exam Question with Answer & Explanation

Johnny has just installed a small utility to calculate subnet masks. After installing this utility he was prompted by his firewall to accept a connection outbound to a server he was not familiar with. Further exploration has revealed that there was a new port listening for incoming connection on his computer. It seems that unwanted software was installed when Johnny installed his great subnet calculator. What type of malware was he a victim of?