Carnegie Mellon's online catalog (accessible from the Library homepage) will let you easily locate books held in our libraries. Books not held by our library can be obtained from other libraries via Interlibrary Loan. A really thorough database of books is called "WorldCat" (look under "State, National and International Catalogs).
Searching a library catalog is different than searching in databases that contain journal articles or conference papers. To get better results, it may be necessary to search under a broader keyword than your specific topic. When you enter a keyword in the catalog to look for books, your search is executed on basic pieces of information like the author, title, editor, publisher and subject headings (i.e. metadata). The book's title and its assigned subject headings assigned in catalog records are often much broader than your topic. Perhaps your topic is only covered in a chapter or grouping of chapters. So keep this in mind and adjust as necessary. You can always ask a librarian for help.
Here are the Library of Congress classification numbers for selected Cybersecurity related topics:
QA75-76.95 Calculating machines
QA75.5-76.95 Electronic computers. Computer science
QA76.75-76.765 Computer software
TK5101-6720 Telecommunication Including telegraphy, telephone, radio, radar, television
HV6251-6773.55 Crimes and offenses
The three library databases below are your best bet for finding eBooks and other digital resources related to Cybersecurity. Most of the materials in these databases should also be "findable" in the Library catalog, but its a good idea to check here as well in case something slipped through.