Depending on the model of your device you can see how many devices are connected to the jetpack. If you only have 2 devices that should show up (ie. tablet, computer) but the device is showing more than that, then you need to log into the jetpack (192.168.1.1) and "boot" them off the jetpack network.
As far as how you do this.....it all depends on the model of the device.
If you hook up a pc to the jetpack then nobody is hacking into your jetpack, its something in the pc that has started using more data. It's nothing you may have done to change it it's just the PC being a PC and using a connection that is available.
Proving that someone is hacking into your Jetpack is very difficult to do. Reason being that you need logs and evidence to support a claim that data usage was consumed illegally or from malicious users. VZW holds the logs that would prove such transactions ever took place, and they wont share that info with consumers without a court order.
Besides, unless the manufacturer comes out and exposes a flaw with the security of the Jetpack VZW is going to say that password security is up to the users to manage. Anyone who has the password can connect and consume internet, VZW cant tell who is a malicious user and who isn't. If you feel you have been hacked then you should do things like reset your Jetpack and configure a new custom WiFi and admin password using standard password security best practices.
You haven't been hacked your just getting screwed like the rest of us. Its like if you go to Account Analysis it says; 10Gb + 5gb overage=$130.00 your bill will say $140.08. The 8 cents is tax. When you call they say OH YOU WERE BILLED FOR A EXTRA GB NOT ON LAST MO. BILL. Then you go back to last mo. bill 10GB+4GB=$120.00 but your bill will say you owe $130.08. You call they say its from a Gb from the previous mo. BLA BLA BLA!! You can't win. And because of the need for a court order, by the time you get a court order the info you need is erased. I believe they only keep 3-4 mo. worth of data.
Best of luck..
I Am having the same problem. Added a Gb for 15.00 ans within a week it was used up. I only use my phone in wifi. I called, and got the same information with no solutions. Turned off my cellular all together. Not sure this will work. Now I have a phone I can't use. I am so disappointed in Verizon.... Now I don't trust them. I'm sad. I feel this company I loved is gouging me. If it was my company , I would be investigating this. If they aren't deliberately gouging us.... Someone is, and it will cost them loyal customers.
Software, Firmware updates on devices also causes the data usage to increase even if you are not using the smartphone, computer, tablet for data. They update in the background. If you are constantly going over your usage monthly you can sign up for a higher data package. Verizon Wireless offers up to 100GB package for $710 a month.