nmap reveals trinoo_master on router

On my Cisco Router, I do a nmap scan from outside on the Internet. The re=
sult is:

" Interesting ports on *.*.50.1:

Not shown: 1676 closed ports
PORT      STATE    SERVICE
23/tcp    filtered telnet
135/tcp   filtered msrpc
1524/tcp  filtered ingreslock
27665/tcp filtered Trinoo_Master

I am worried about the last two entries. The last nmap was done in Feb th=
is year and I have confirmed that the two port entries (tcp 1524/27665) d=
id not exist then.
Though the port state "filtered" is a solace but I am still concerned. Ho=
w can I be sure that the system has not been compromised?

Also the current IOS Version of my Router 2811 is 12.4. It was the same c=
ase with open ports when I was using older Router Series 1700 v 12.2, so =
I thought maybe, it's an IOS issue and I upgraded my Router to 2811 with =
IOS v 12.4 yesterday. But as soon as I plugged it into the circuit and di=
d a re-scan, I realised the nmap again gives the trinoo_master entry with=
 state as filtered.

Where could lie the problem. Is it with my firewall (PIX 515) configurati=
on behind the router?
Please Advise!!

I have seen Cisco's tech doc that exists here:
http://www.cisco.com/en/US/partner/tech/tk59/technologies_white_paper0918=
6a0080174a5b.shtml

One of the solutions suggested therein is to implement "ip verify unicast=
 reverse-path" on the serial interface, but am not sure what will it serv=
e? Also, I suspect that I had other problems when I gave this command so =
I reversed it.

"sh process cpu" only shows cpu utilisation of about 5-6%.
Please advise!!

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