I just read this article which I find concerning:
"After 90 minutes of troubleshooting, Nash traced the problem to TeamViewer, which he used to remotely administer the client's servers. It turns out the program had opened up its own webserver on the client's machine as soon as Apache went down and in the process made it impossible for the client, a large provider of business software, to restart its proper website."
http://www.theregister.co.uk/2009/07/24/teamviewer_snafu/
I started using TeamViewer recently because it's just much better than UltraVNC (runs on both XP and Vista, the server dials out instead of requiring the user to open a port on their router + better performance than UVNC)... but I thought that TeamViewer had both the server and client connect out to TV's web server for data to flow between the two hosts.
Why does TV even need to open a web server on the server host?
Ports 80 and 5938 are used by default for TeamViewer's DirectIn -feature, which enables faster connection openings by trying to configure a NAT route automatically by using UPnP.
You can disable the DirectIn performance optimizations from TeamViewer's options menu in Extras -> Options -> Advanced -> Show advanced options and by unchecking the "Enable DirectIn Performance optimization".