Although gaining access to another person's system is illegal in most countries, law-enforcement agencies and some companies have been using Remote Access Trojan (RAT)–like intrusion tools for years. In the United States, the FBI and other law-enforcement agencies can get a court order to use RATs as criminal-investigation tools. US corporations don't have to warn their employees that they're using RATs and can collect data without end-user authorization.

Last year, the FBI revealed that it uses a RAT, code-named Magic Lantern, to conduct surveillance missions. Although the agency initially denied Magic Lantern's existence, the FBI later acknowledged its use of "RAT-like products". WinWhatWhere's Investigator 4 is a RAT that companies and law-enforcement agencies have used since 1993. This program features keystroke logging, WebCam and screen captures, and log file and Internet activity, and can be activated based on predefined events. The program can even hide itself using different filenames and move around the system in an advanced game of hide-and-seek. For $100, without a court order, you can buy it and use it any way you want. Although such use is illegal in most US states, Investigator is a popular choice for spurned spouses and private investigators who are looking for evidence of adultery. Since 1998, Codex Data Systems has produced a $2000 law-enforcement key-logging trojan called Date Inception by Remote Transmission. D.I.R.T. can reportedly get around software-based firewalls and has remained undefined by antivirus scanners because of its rarity. However, at least one public security firm, Diamond Computer Systems, has conducted an extensive analysis of the product and says D.I.R.T. doesn't live up to its hype. (To view this analysis, go to http://www.diamondcs.com.au/web/alerts/dirtanalysis.htm.) SpectorSoft produces Spector Pro, which has all the features of Investigator and D.I.R.T. plus the ability to send alerts and record activity when someone types predefined keywords (e.g., "I hate my boss") in an email message. Spector Pro advertisements brag about the product's ability to remain hidden: "It doesn’t appear in the Windows System Tray, Desktop, Task Manager or in the Add/Remove Programs menu."

Clearly, technology has the ability to easily invade personal privacy. The question is whether such invasion is legal. In the case of most RATs, the answer is no.