Check your Router's SOCKS service first. If you have never used a SOCKS service on your router, make sure it is disabled. If not, this means your router has been compromised.
SOCKS is a proxy server that allows the relay of TCP-based application data across a firewall, even if the firewall is set to block packets. The SOCKS protocol is independent of application protocols and can be used for many services, e.g., WWW, FTP, TELNET, and others.