The answer lies with the site you are downloading from. Major abandonware sites like MyAbandonware and Abandonia are safe, serving thousands of users every day.

Is abandonware free to use?

In this case, yes, abandonware is illegal because while you couldn't actually go out and buy the game even if you wanted to, the copyright is still owned by Lucasarts. Lucasarts might choose to make the game available for free (making it freeware), but probably not. If you download it, it's technically piracy.

What is considered abandonware?

Abandonware is computer software (such as an operating system , word processor, interactive game, or audio file) that is no longer marketed or distributed by the company that created it, but is obtainable from some other source.