So let me ask a hypothetical.
Had the OP:
Created a EULA that had to be agreed to before installing that spelled everything out.
Included a "Phone Home" function that would allow him to, on a remote server, give software a "thumbs up" or "thumbs down" for valid use.
Would he then be within his legal rights to simply switch that install of his work to "thumbs down" and disable it?
Joe
The OP in this case was an employee; under most employment contracts, the employer owns all the code and all the rights to grant licenses.
However, in the hypothetical situation of the OP being a contractor selling a software product, it may be possible to disable the software.
I know of one case where it was done, the client was a large B2B retailer with a number of sales outlets and a number of warehouses in different parts of the country. They hired a small company as a contractor to produce an electronic stock/sales/communication system to replace having to do everything between warehouses by phone/fax.
The contractor had a lawyer draw a contract where the use of the software was subject to a monthly time-limited license which would be renewed by mutual arrangement between the buyer and the contractor. Once the final milestone had been signed-off and payment received the license would be transformed into a perpetual license.
The guy had worked for about 6 months, and had met the interim development milestones, where he had received some token interim payments. However, he had pretty much finished, and the software was fully functional and there was no further development planned, just bug fixes and minor tweaks. At final sign-off he would receive the final balloon payment for the software.
It was at this point that the customer tried to stiff the developer. They were now using the software in production, they'd abandoned all their old registers for PC terminals running the software, they'd received an e-commerce website as part of the package (and this was now responsible for a significant amount of new business), and all the warehouse tracking/auto ordering/dispatch stuff was in place, and the old paper/phone/fax system had been dismantled.
At the final sign-off meeting, they basically said, that they no longer wanted any development services and they were firing the developer. "OK", he said, "but I will require you to cease using the system by the end of the month."
The client continued to use the system, until the end of the month at which point the license expired; every component of the software had been programmed with a time-limited license key. When the key expired, all the registers, consignment tracking, warehouse stock monitoring, communications tools (including VoIP phones) and the e-commerce website shut down. One hour later, he had a motorcycle courier turn up with a stack of $100 bills (actually, it was probably a certified bankers check) representing the final balloon payment.