Selling viruses? Is it illegal?

I am a programmer looking to start a business where I create programs that employers can install on their computers. Nearly identical software is often used nefariously by hackers. Even when being used in a legal way the software still acts very much like a viurs. I am wondering if selling this software would break any state or federal laws. Of course I know that hacking with viruses is illegal, but I'm not sure that selling viruses necessarily is. Employers can use software, such as keyloggers to ensure that their employees are using computers acceptably during work. Even though hacker's can use keyloggers to gain sensitive information unsuspecting victims, an employer can use one on a computers they own. I would ume that the person or the company selling the software isn't liable for the actions of their customers, the same way Wall-mart isn't responsible if you murder someone with a knife that they sold you instead of using it for it's intended purpose of preparing food. I am wondering if my hypothesis is correct. If so, are their laws (federal or state) and/or court rulings that regulate this market that I, as a Illinois citizen, should be aware of? Am I obligated to verify that the purchaser does not have a malicious intent? And are their limits to the features of my software? Also, because much of my business would be done online; am I obligated to follow regulations created by other states, and even countries? If anyone knows the answer to these questions, or where I could find - if they exist - regulations, especially any applying to Illinois and the United Stares, I would greatly appreciate it. Thanks.