The University of SydneyPage 17There are bad guys (and girls) out there!Q:What can a “bad guy”do?A:A lot!–eavesdrop:intercept messages–actively insertmessages into connection–impersonation:can fake (spoof) source address in packet (or any field in packet)–hijacking:“take over”ongoing connection by removing sender or receiver, inserting himself in place–denial of service: prevent service from being used by others (e.g., by overloading resources)