Yes, It is very illegal.
You would be charged with "Unauthorized access to a computer network", which in most states is a felony. There also could be other charges too, like theft of service, etc.
There are many reasons why it is so risky to have an unsecured network. The problem is that most people who install wireless networks have no clue about security, so they leave their system "wide-open". This does not make it legal for you to jump their signal though. Using their wireless system to access the internet is stealing. Many states are prosecuting more and more people for this as it is a growing problem.
Keep in Mind when you have a wireless system:
You are leasing this service through your provider, and are responsible for its PRIVATE usage. Many Internet providers have canceled customers due to high usage from wireless signals that are used by the whole neighborhood!!
- Linking to a unsecured network, leaves you vulnerable to criminal charges, as well as your system being hacked, viruses, etc.
- When you log into someone else's wireless network, the IP address you use, is theirs!! So anything you do online is making it their responsibility as well and will be traced back to them, and then to you. You could also be sued for any damages caused by you using their system.
- IP addresses are like DNA or a FINGERPRINT on the Internet. This is why you need to protect your wireless system and keep people from signing on to your system.
- Leaving your wireless system unprotected leaves you open for illegal activities, viruses, and all your computer information available to the world.
- Good Example: If you have a wireless system unsecured, and Joe Smith down the street uses your signal, he uses your wireless network to access child pornography; your provider throws a flag that child pornagraphy is being looked at, distributed, etc.; they report YOUR IP to the FBI; the FBI comes and raids your home, computer, and charges YOU with child pornography. If you are lucky, weeks later, police computer experts may discover that your computer was not involved and that it was Joe Smith down the block, but by then, your reputation is ruined. Do you really want to have your name all over the news for being raided, EVEN if they clear you weeks later?
- SECURE YOUR SYSTEM! DO NOT USE ANY WIRELESS SYSTEM, UNLESS YOU HAVE PERMISSION.