This depends on your particular situation, but let's start by saying that Web-based will work in any situation so to test if you've configured everything correctly you could start by selecting that one.

But now for the actual explanation. You should only choose Modem or LAN if your computer is directly connected to the internet and has a publicly accessible IP address. If you're behind a firewall or using a NAT-capable router or access the internet using an ADSL or Cable Modem you will must likely not have a publicly accessible IP address. The only option left will be Web-based udates.

So what is the difference? Well with the Modem and LAN update methods DeeEnEs can detect any changes in your IP adress almost instantly while the Web-based method can take up to 10 minutes in a worst-case scenario (see question #2 below). If you add to that the normal delay of the internet when you change IP addresses (see question #3 below) it can take almost half an hour between the moment your IP actually changed and the moment everybody in the world can access your domain again.

You are probably using the Web-based update method. When using this method DeeEnEs periodically checks with an external server to see if your IP address has changed. To prevent DeeEnEs from putting too much strain on that server it will never check more than once every 10 minutes. So in a worst-case scenario it can take up to 10 minutes before DeeEnEs notices that your IP address has changed. If you are really sure that your IP address has changed you can select Force Update from the tray icon's pop-up menu.

This most likely has to do with the way the internet works. Changes to IP addresses take some time to propagate around the world. You can read here what the people over at DynDNS have to say about it.

The first thing you can do is check what your computer thinks is the IP adress if your domain. To do this you can open a Command Window (select Run... from the Start menu, type cmd and click Ok) and type ping yourdomain.dyndns.org. You should change yourdomain.dyndns.org to the domain that you registered of course. You should get an output looking like this:

Pinging yourdomain.dyndns.org [nnn.nnn.nnn.nnn] with 32 bytes of data:

Reply from nnn.nnn.nnn.nnn: bytes=32 time=18ms TTL=249
Reply from nnn.nnn.nnn.nnn: bytes=32 time=18ms TTL=249
Reply from nnn.nnn.nnn.nnn: bytes=32 time=27ms TTL=249
Reply from nnn.nnn.nnn.nnn: bytes=32 time=15ms TTL=249

Ping statistics for nnn.nnn.nnn.nnn:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 15ms, Maximum = 27ms, Average = 19ms

Where nnn.nnn.nnn.nnn is the IP address that is connected to your domain according to your computer. Now compare that with the IP address you get when going to this page. If they are not the same you should double-check your account settings in DeeEnEs and see if it really updated. Check this by going into the Accounts dialog and selecting the account: the enabled option should be checked and the message in the middle should say Updated successfully with a recent date. Try selecting Check now from the tray icon's pop-up menu to see what happens. Check the log window for any errors or other message that might explain what is going on.

If the two IP addresses are the same DeeEnEs works perfectly and there is probably some other reason for your problem. The most likely problem that many people encounter is that they are trying to run a web or FTP server on their computer but can't access it. The reason for this most of the time is that fact that they are behind a firewall (either on their own computer, on their network or even their ISP) that is blocking incoming traffic from the internet. It's outside the scope of this FAQ to explain how to solve those problems. Try Google or a friend with some good understanding of firewalls and such.

You are probably trying to copy the new DeeEnEs.exe over the old one while it is still running. This is not possible in Windows (it is not Linux afterall) so you first have to exit the currently running version DeeEnEs before copying the new file. To do this just right-click on the DeeEnEs tray icon and select Exit from the menu. Now copy the new DeeEnEs.exe over the old one and re-start the program by double-clicking it.
If you can't remember where you left the old version, don't worry, just copy the program to any location you want and start it. This will ensure that from now on the new version will be used. If at any time in the future you come across the old version again you can safely delete it.

DeeEnEs does in fact have the capability to run as a service. It's just not advertised because it still doesn't work like it should. Why? Well, you can't change any of its settings while it runs as a service for example! So the only option would be to run it normally, make sure all the settings are okay, exit and then install it as a service. Installing it as a service is easy, you just start it from a command line with the option /INSTALL But if you need to change anything you will need to stop the service or even uninstall it (using /UNINSTALL), run it normally, change the settings and reinstall as a service. As you can see this is not very user-friendly. But if you really want to you can go ahead and use it.