Only if they distribute it. What people don't often realize is that GPL (both v2 and v3) has a "trigger" condition, where the GPL reciprocity applies only with

Only if they distribute it. What people don't often realize is that GPL (both v2 and v3) has a "trigger" condition, where the GPL reciprocity applies only with physical distribution of the code. As an end-user, it's perfectly fine to modify GPL code and keep the changes private.