http://grc.com/su-evilportmon.htmOk I did some research on port 25 SMTP... It turns out that port 25 is used to send mail...  If you are using a mail client like outlook express or endora, I guess, and your ISP doesnt give you a url to log into you mail, mail.yourisp.com.  The reason that port 25 came up as a security problems in that port scan  is because that is generally how most of the SPAM get to your computer.  Most of the ISPs are not blocking that port for their customers so that SPAM is reduced...  If that port is open my only suggestion would be to put a router with a firewall on it inbetween the modem and your computer.  As of right now I can not find a way to shut off that port... other than to install a router firewall..  I ran a scan on a different site and I can up with nothing open... I also recieve no spam to my computer...  The idea behind port 25 is that all the spammer has to do is ping your ip address... see if port 25 is open... then start sending you all the free stuff you dont want.  

Here is a basic place that explains this in more detail.. http://grc.com/su-evilportmon.htm   Here is a decent "port blocker" http://www.analogx.com/contents/download/network/pblock.htm

The only other thing that i can think of is to go into the router software and make sure that you dont have port 25 opened by accident...  You also might want to check for spyware...

I surfed over to linksys and looked around a bit... I also looked at some manuals...  Under UPnP forwarding.. in the web utility that Linksys provides with the router is a list that has all of the common protocalls... disable smtp.. that should take care of that port..  However, you might loose the ability to send mail...  So you can either see if your isp has a pop3 address or if there is a different way to connect to get to your mail...  If neither are true then you are just going to have to turn it on when you need your mail and then turn it off.. it is really hard these days to secure a computer to the point where it totally invisible on line.  If that is what you are after you mind as well put your computer into a vault remove the 3.5 drive and cd drives and never connect to the internet...  Pretty boring...     Give that a try also what model number do you have of the linksys router?