Windows servers have background processes that perform many functions, called services. Unix systems also have background processes that work in a similar manner that are called daemons. Regardless of what you call them, these processes, which are called background because they do not require interaction with the keyboard but instead execute on the computer waiting to perform some function, can introduce security problems when they are not needed.
You should become familiar with the background processes on any servers in your network and disable those that are not needed. For example, on Unix systems, there are many background daemons associated with the TCP/IP suite of protocols. Some systems might need all of these, whereas some might need just a few or none of them. It might be that you do need these services. It might be that they need to be configured properly prevent their misuse. You should read the dumentation that comes with your Unix or Linux system to determine the capabilities that these daemons provide and disable them on systems that do no need them.
For example, tftp (the trivial ftp transport application) is a stripped-down version of FTP. It is com and usually can be easily implemented in an EPROM. For this reason, it is useful in some devices need to download operating software from a host. However, note that unlike FTP, tftp has no acc control mechanisms. This means that a username and password are not used. Because there is no authentication, this can be a real security problem if it is not configured properly, such that it can used only for its intended purpose.
On Windows servers, you can use two programs that are provided with the Resource Kits to install or run almost any executable program or batch file as a service. These are INSTRV.EXE, which can be used to install an executable, and SRVANY.EXE, which can be used to make other kinds of files into services. On a server that has several users logging in frequently, you might want to make it a regular part of your routine maintenance to review the services running on the machines and disable or remove those that are not installed by the initial operating-system installation or those that did not come from products you have applied to the system.
To do this, you will need to keep an inventory of what runs on each server, but this kind of inventory information can be useful for other purposes, such as when you need to reinstall a server that has been destroyed by a catastrophic failure.
Removing Dead Wood
Every operating system comes with default options installed that you might not be aware of unless you have read the documentation carefully. For example, default user accounts might be created
when you install the OS or later install a product. For example, the GUEST account in Windows operating systems is installed by default. You should always disable or remove this account. The Administrator account is also a vulnerable target because it is present on all Windows Server computers from Windows NT through Server 2003. You cannot delete this account, but you can rename it so that the hacker's job becomes more difficult. Also, you shouldn't use the Administrator account on a regular basis. Instead, create individual administrative user accounts for each system administrator trusted to perform these high-level tasks. Then put them into the Domain Admins group to allow these users to exercise administrator privileges, while maintaining an audit trail of the actual users who performed certain actions. You should always use separate administrative accounts for your domain administrators. Never use the same account for domain administration as is used for regular user functions. Administrators should be logged in with administrative accounts only when performing activities that require elevated permissions. You can also use group policies to further restrict what each user can do.
Regularly review the user accounts that exist on the network. Use the auditing features provided to determine when an account has not been in use for a long period, and if you can find no reason for its existence, disable it. Maybe someone in another department did not notify you when a user was terminated, or maybe an account was created for an expected new employee or contractor who later changed his mind and did not come on board. New accounts such as these are typically created with a simple password and can leave gaping security holes in your network.
Old programs and files that are no longer needed, or the use for which you are not sure, are also easy targets to cause security problems. As a rule of thumb, if it's not needed, back it up to tape and delete it! If a user finds that something she needs is missing, she will tell you!
When installing a new application product for a user, be sure you know the capabilities of the application. Don't install unneeded optional features that will not normally be used. Read the documentation!