Monitoring the activity of people is starting to enter questionable legal (not to mention ethical) grounds. How can you stay on the right side of it?
Know your legal requirements, be ethical, and you are unlikely to get burned.
It is hard to write a section that will comprehensively cover all areas in all countries; each legal system has its own statutes and acts that apply to the area of computing. To give this section a fair appreciation, we are going to approach it from an ethical standpoint. There are sections of U.S. and U.K. law referenced in the "See Also" section at the end. To quote them would probably be counterproductive, as they are likely to send you to sleeptrust us, we've read them.
It is ethically wrong to spy on someone without good cause. In the case of detecting an attack or an attacker, your good cause is the protection of your business or personal assets. This is fairly simple, but you would still do well to include a banner to this effect at any point of access (e.g., FTP, web server, Telnet, SSh, etc.). Something along the lines of:
----- This is Simon's FTP Server. ----- Unauthorized access or unauthorized use is not permitted. All use of this server is monitored for security reasons.
This quite clearly states that access is only for those authorized and that usage should also be authorized (so an employee uploading the latest Star Wars movie is also subject despite being authorized for access), and that all such usage is being monitored. It also states the reason for doing so. If you feel like adding a bit more emphasis to it, you can always add:
Anyone found to be in breach of authorized use will be prosecuted to the fullest extent of the law.
It doesn't really add much legally, but people might think a bit more if they think you might actually do something about it!
Legally, you are going to do pretty well against someone who is attempting to compromise the security of your systems.
"Your honor, my client's privacy was invaded while he was exploiting a buffer overflow to deface the web site of the plaintiff."
In most (but not alldon't count on it) countries, this is a criminal offense in itself. However, your own employees, and even your legitimate customers, are in a very different situation.
There is a significant difference between "attack" and "misuse," as the previous FTP server/Star Wars example shows. As an employer, you need to define an acceptable use policy before you can monitor for acceptable use. If you don't tell your employees what they can and can't do, you can't realistically expect them to know. You should be aware that the emphasis is on getting them to read the policy; ideally, you should have them sign a hardcopy of the policy and then keep it on record. This should be kept up to date, reissued, and hopefully re-signed. The time scale for this is dependant on your business, but annually is a good bet. Obviously, this doesn't actually mean that anyone reads the thingthey just sign it and get back to workbut it does give you a position of far greater strength. A reasonable acceptable use policy is available for download from http://www.sans.org/resources/policies/; there are also a lot of good guidelines here for other areas of policy implementation.
If you are keeping information on computer, and this information could possibly be related to the actions of an individual, which they may be within IDS logs, you should be aware of your obligations under any personal data laws that may be in force in your country. A company once had issues with getting billing information for their software from another country, the billing records matched a username with duration of use of the software, and this was determined to be enough to identify an individual and prevent that data from being exported. Ensure that you either use the obfuscation feature until completely necessary, or are allowed to keep such information in order to avoid problems.
Installing Snort from Source on Unix
Logging to a File Quickly
How to Build Rules
Detecting Stateless Attacks and Stream Reassembly
Managing Snort Sensors
Generating Statistical Output from Snort Logs
Monitoring Network Performance