Manage activations by entering your license key:

License is valid indefinitely for the major (4.x, 5.x ...) version you purchased it for. That same license is also valid for one year from date of purchase for any other major version.
See all licensing details in End-user license agreement (EULA).

License Upgrade has lower cost than buying a completely new version and can only be done from the immediate previous major version. For example, you can upgrade from 3.x to 4.x or from 4.x to 5.x but not from 3.x to 5.x. Going from 3.x to 5.x requires a full license purchase.

Unlimited VMs mean that you can activate SSMS Tools Pack on any number of Parallels, Hyper-V, VMWare, Xen or VirtualBox virtual machines. The VM check can return both false positives and false negatives in about 0.1% of cases. Please let me know if that happens.