Aalto provides an professional» site license to all the community. For more information, see https://www.overleaf.com/edu/aalto.
In order to link yourself to Aalto, you must register for and have an OrcID [wikipedia]. An OrdID (“Open Researcher and Contributor ID”) is some permanent ID which is used for linking researchers to their work, for example, some journals require linking to an OrcID. OrdID can be accessed directly with your Aalto account.
TODO: determine exact procedure and update here
Aalto rates overleaf as for “public” data. This doesn’t mean that Overleaf makes your data public, but just that Aalto can’t promise security. In reality, you decide if Overleaf is secure enough. If there is some legal requirement for security, you probably shouldn’t use Overleaf. If there is a collaborator requirement for security, then you must make your own choice if Overleaf is suitable.