nmap -PS -PA -PU flags

[seven]

Hello!
I have a question. I bought fyodor's book for NMAP and it's been great! I am really learning the internals and best practices. But one thing i'm confused with is the host discovery flags PS PA PU. Syntax should be P[A/S/U]<port list>
Essentially, it should be probing for hosts sending either SYN,ACK or UDP probes to the ports suggested. However, when I use it, I detects hosts that are up but on ports I didn't specify.
E.G. @my house
nmap -PS80,21,25 -PA80,21,25 -PU53 192.168.1.0/24 -v
will yield results for my http server,ftp,dns but also scan ports up to 4444 and higher.
Any reason this is happening? Am I using the flag wrong?

Thank you.

[Lincoln]

Try separating the ports with -p.

ex: nmap 192.168.1.1 -PS -p 21,25,80 -v

[thorin]

You're doing it the right way. The thing is the scan isn't limited by those probes/ports. After doing PS/PA/PU it still does the normal run of the default popular 1000 (or 1287) ports. If you don't want nmap to do that then you have to limit the ports to scan with the -p as Lincoln suggested.

[Ermak]

The best choice is to use those discovery flags with -sP parameter, so it won't start SYN scan on active systems.