Port scan from Apache?

[Clemens Renner]

Hi everyone,

today I got an e-mail from a company claiming that my server is doing 
port scans on their firewall machine. I found that hard to believe so I 
started checking the box.

The company rep told me that the scan was originating at port 80 with 
destination port 8254 on their machine. I couldn't find any hints as to 
why that computer was subject to the alleged port scans. Searching in 
logs and crontab entries did not reveal the domain name or IP address of 
the machine except for my web mailer. It seems that someone from the 
company's network is accessing the web mailer in 10-15 minute intervals 
which is absolutely believable since one of my users works for the 
company and checks his mail via the web mailer. The strange part is that 
the company rep said these scans started some time on Sunday, while my 
user definitely was not using the company's hardware.

Apparently, the company uses NetScreen hardware and/or software for such 
intrusion detection / prevention mechanisms and the log he provided read:

[Root]system-alert-00016: Port scan! From $my-server-ip:80 to 
$their-server-ip:8254, proto TCP (zone Untrust, int ethernet1). Occurred 
1 times.

My questions are:
1. Can this be malicious code on my side? Both port 80 and 443 are bound 
to Apache's httpd so they shouldn't be available to other processes, right?

2. I'm using ipfw as a firewall where everything is denied except for a 
rather tight permitting ruleset that (of course) allows communication 
to/from port 80/443 on my machine but not to the destination port 8254. 
If the firewall prohibits access to a remote port 8254, processes on my 
side shouldn't be able to initiate a connection to that port. If there 
is a connection to that port, it had to be established earlier by the 
remote machine. Am I correct?

3. Does anyone know when the NetScreen hardware / software labels 
something "port scan"?

As far as I can tell, the server is free of malicious code, I especially 
looked for PHP (and similar) files belonging to freely available port 
scanners etc.; everything seems to be alright. While I was 
investigating, no one but me was logged in.

Any help is greatly appreciated!
Clemens