I have been contacted by someone who is obviously not interested in the CAD stuff.

Report here and attach that screenshot with the report.

Hello IT security I think you have a problem

My thoughts are that this is an ongoing problem from lack of verification controls for signing up as a member. It seems that the desire to build up membership has foregone security controls. Why is there 8.5 million members yet only 4.54 million CAD files and if you take into account contributing members with multiple uploaded models, then the ratio for active to parasitic members increases dramatically.
I realise some members would prefer to remain incognito however there should still be controls to confirm identity of a member to the GRABCAD organisation to help police illicit activities on this site. Without such anyone has a cloak of invisibility and can create new identities easily to continue with their nefarious activities. It would also give a greater sense of confidence that as a member that you are interacting with a likeminded engineering colleague. Regards M.Bruton