With the vast majority of open source software licences (including the GPL) you're perfectly entitled to integrated it into your propriety code without releasin

With the vast majority of open source software licences (including the GPL) you're perfectly entitled to integrated it into your propriety code without releasing it if you're not distributing it externally. The only exception of any size is the Affero GPL but even that only applies if you use the code in an external customer facing service.