Your IP address. None of the above. To get past a firewall, a cracker might program his computer to look like it has your IP address. Sequence number prediction. LAN identification code.
Computers are less expensive.now.
Computers are more powerful now. Both a and b above. None of the above. The inclusion of Secure ID Cards and firewalls practically guarantees that your network will be secure against attacks by crackers. Surveillance is just as important as, if not more important than, a firewall in a complete network security package.