In the United States it is illegal under the DMCA (Digital Millennium Copyright Act) to break any form of Digital Rights Management (DRM) to enable software features you didn't pay for.
The exceptions some have mentioned here do NOT apply to unlocking features that are not paid for. Someone also asked if there was a license, and again, that is not relevant — The bright line is that it's illegal to circumvent DRM to activate software you didn't pay for.
EU nations are subject to the WIPO treaty, which includes DRM. I am less familiar, but there is a WIPO site with a great deal of information.
OP @Atizs said:
As I see it - I bought the tool from them, and since the software was already on there, I am free to do what I please. I understand their intent, but since I paid for the device, which already had the software on it, and I just accessed it, I do not think it qualifies as theft. The moment they handed me receipt, I have ownership of the device and everything on it, right?
You have ownership of the HARDWARE, and the right to use the software as enabled at the time of purchase, or per some specified agreement. You do not have the right to circumvent Digital Rights Management to activate unpaid for features.
Similarly you do not have the right to download the software and distribute or sell it, though you CAN sell the whole device as purchased.
Many software packages have locked features that require an additional fee to unlock. For instance, Adobe allows you to download their entire suite of applications free, but you have to pay to activate them.
In the example of multimeter A or B, and you purchased the one with fewer features at a lower price, but then hacked it to unlock software you didn't pay for, it "sounds like" you circumvented Digital Rights Management software, which is illegal for the purpose of activiating software or features not pay for.
HAVING SAID THAT
What did you have to do to "access" their software? Did it involved cracking any sort of encryption or digital rights management? Under the US DMCA, if you activated the software by circumventing or hacking or disabling DRM, it is against the law.
WIPO also has clauses that prohibit circumventing DRM, I am less familiar.
But if the device could have those features turned on and there wasn't really a DRM protecting them, that may be different. Without giving exact instructions can you say generally what you did? Did you JTAG the device? Download the code from the mpu and alter it? Solder jumpers that changed configuration??