The basics are this:
1- it is not ilegal to have listing of links that point to copyrigthed material. There have being several atepms to have this ilegal, the last one was the so call SOPA, and it fail, have it pass there would not be google today.
2. The website is not responsable for what people post, they do moderate, but they are limited to their resources. So as long as they have some line somewhere saying they no responsible and they do efords to cooperate with the owners of the material, when brough to the attention of the website, then there is not problem. So for example users upload pictures on the forums, profile pictures and so on... many of those files are not open license and most likely someone, somewhere, have the rights for them, as long as they are user uploaded, it is not iligal for the website to host those files. As long as they take them down accordenly to standard legal practices.
2. Some users dont care about copyrigths, they will freely share as they want, and they don't care and/or don't know about the legal status of each single file.
3. The owner of the infrigting material can take legal action, this is trough a DMCA, wich is a very simple procces on wich the owner of the material will send a "take down" notice to the webmaster, and the website staff will consider the situation, more likely they will disable the information to public access and contact the user who posted it to see if he want to counter the DMCA, usually they don't counter, but eventually someone does. Whae happend in most cases is they leave until someone else post the material againg, or the same person with diferent account name post againg. As this can turn out to be a very constant situation, when website reach certainly size they will have staff members dedicated only to this job. However it is, websites (as many companies do) usually work on the basis of dealing with problems when they apear, than preventing the problems to happend.
3. If the person decides to counter, for example knowing that the copyrigth expired or so (there is a lot of exeptions to copyright, and a lot of tricky legal wording on it)... in this case the person sending the "take down" notice can face serius legal consequences, as in being accused of filing a fraudulent DMCA to restrict the first ammendment right of someone.
And this is the reason why in many stances they will not file up DMCAs bacause if successful it will take down the material for some time, if fail it will potentially means years on prison.
Is it legal or illegal for sites to have free downloads of chess books. I am new to this site and coming back to chess after 40 years. I am surprised so many downloads are available for free for chess books. What gives in this world? No one respects copyrights? I keep seeing links to downloads on here that I never thought would exist. If I wrote a chess book and 6 months later someone has it on their web site I would be very angry and seek legal action. I guess having eBooks facilitates this in a way that it is already in electronic form.
Maybe someone can enlighten me.