Opening one of the dll's in C:\Qt\Tools\OpenSSL\Win_x64\bin with e.g. Dependencies.exe (https://github.com/lucasg/Dependencies ) or another dependency analyzer shows which libraries these dlls depend on.

One of these dependencies is MSVCR100.dll, meaning that the libraries have been built with MSVC 2010. This means that every application using these files gets an additional dependency to the "Microsoft Visual C++ Redistributable 2010" package.

In order to avoid that a Qt application depends two different C++ runtime environments, OpenSSL should be built with the latest MSVC version that Qt itself currently uses, so there is at least a possibility to avoid this additional dependency.