If someone a) finds my calibre-web installation on the public internet b) manages to crack my username and password to log in c) scan the contents d) notify the correct rights holders e) send a subpoena for pirating content
Accidentally? My calibre-web is actually exposed online :P
It doesn't list any books that I have publicly though. All you'll see is a login prompt. Books? what books? You can't DMCA me because I only have gutenberg collections in there ;)
...they can get my money.