above: John Garfield in He Ran All the Way
The blacklist of people suspected of harboring "un-American" attitudes or politics drove a lot of talent--especially writing talent--out of Hollywood in the late forties and early fifties. Still, movies need and writers, and writers have to work, so blacklisted talent like Dalton Trumbo and Carl Foreman either wrote under fake names or paid friends and/or colleagues to serve as 'fronts.'
In recent years, some of these writers have had credit given to them--often posthumously--on projects where they did most (sometimes all) of the writing. Here's a link to a list of corrected credits, many of them notable noirs.
For a case study of the Hollywood blacklist, here's a link to my essay on the making of He Ran All the Way, a noir at the center of the furor.