> Thank you for reaching out to us. From time to time our titles may become available to the public for legal download. There is no guarantee that titles available will remain available permanently. The only titles that will remain available are titles marked as Open Access.
Thus, it sounds like what happened was an accident or publicity stunt. I expect access to remain cut off.
In particular, I am teaching a course this spring based on two Springer books that I was able to download yesterday. If I e-mail PDFs to all of my students, am I legally in the clear?
I am quite annoyed by this revert -- especially by the fact that big publishers can generate so much good will just by a simple error that gets shared on the Internet, while the correction will get minimal exposure.
If there's no license specified, default is "all rights reserved" and you cannot distribute the books to your students free of liability.
1.2 You may solely for private, educational, personal, scientific, or research purposes access, browse, view, display, search, download and print the Content.
1.3 You may not: [...] re-distribute, reproduce, or transmit the Content by any means including electronic (e. g., via e-mail) nor post it on their personal or public websites or on public networks...
So while you may have the copy of the book legally, it seems unlikely that you can give it to your students. There's always a chance that what they're saying isn't legally enforceable (see non compete agreements), but I don't think that's the case here. I'm not a lawyer, so I can't say for sure.
Examples of working links: http://link.springer.com/book/10.1007/978-1-4302-5927-5 http://link.springer.com/book/10.1007/978-1-4302-6131-5 http://link.springer.com/book/10.1007/978-1-4842-0100-8
The content identified by the original post were not open access; they were paid access (typically quite expensive) and published in 2004 or before.
I hope the zero cost downloads was not a glitch but a policy, and that Springer will make those older texts freely available again.
If I had to guess, I'd say a pretty good chunk of them already were on torrent sites or LibGen.
So, I suggest you have a look into this and see if you can also get access via the academic login page and Shibboleth or Athens. Or, if not available to you personally, you may be able to just go to your nearest university library and get access to the books that way, too...
OP link lists 66,327 results (i.e. books) available free of cost.
EDIT: no, I was mistaken. I can "download PDF" but it looks like that's typically only introductory content and not the entire book.