Question : Port scanning: what would cause it from a PC?

A client is being blocked about once a week from our (LAMP, Cpanel, with IFD firewall) server because of Port Scanning.

What in a PC would cause port scanning from his home isp connection, and how to curtail?

thanks!

Answer : Port scanning: what would cause it from a PC?

If it is really port scanning, its a virus, trojan and the computer may be part of a botnet.  If that PC and/or that user has access to any sensitive information, I'd deny access until it is cleared up.