All of a sudden I’m getting these:
from Zone Alarm an average of once every six minutes, all from different IP addresses, and aimed at various ports. In the past I hardly ever saw these.
What is the purpose of sending requests like these? Why are there so many of them all of a sudden? If this is someone trying to break into my computer, is Zone Alarm enough to keep them out?
Try this link:
http://www.robertgraham.com/pubs/firewall-seen.html
By a quick glance, it does not mention the exact, specific problem that you are having, but it has some other good info that may help you nonetheless.
Looks like some ankle biters are trying a broad spectrum to see which machines they can break-in.
Make that “broad spectrum scan”
It’s likely that script kiddies are scanning massive blocks of IPs looking for security holes as Urban Ranger points out, but you could also have a trojan horse sending out the “I’m here” signal.
I highly recommend Swat It to scan your machine for Trojans. It does a much better job of this than Ad Aware or traditional virus programs like Norton and McAfee.