Trojans???

[Huh?]

I've recently had my PC fixed and when the technician was here, he took notice that my IP address was being pinged like hundreds of times within a half hour. I have Zone Alarm and I have it set up to do it's thing automatically so I was pretty much unaware of this problem. The tech suggested that I call Comcast and have my IP address changed. I called Comcast and they told me that they use "dynamic" IP addresses and that they change every so often automatically. The tech that was at my house, also said that he suspected that I might have a Trojan.

1. What is a Trojan?
2. Why wouldn't my SpyBot pick up a Trojan if I had one.
3. How do I find out if I have a Trojan?
4. What can I do about it if I DO have one?

I already have Norton 2000, AdAware, and Spybot.......

5. What the heck else do I need.

[andyms18a]

go to this site and press start scan http://www.anti-trojan.net/en/onlinecheck.aspx

[Huh?]

Thanks.