Which mode of IPSec should you use to assure security and confidentiality of data within the same LAN?

What kind of detection techniques is being used in antivirus softwares that identifies malware by collecting
data from multiple protected systems and instead of analyzing files locally it's made on the provider's
environment.

Which of the following is a vulnerability in GNU's bash shell (discovered in September of
2014) that gives attackers access to run remote commands on a vulnerable system?

The "black box testing" methodology enforces which kind of restriction?

The network in ABC company is using the network address 192.168.1.64 with mask
255.255.255.192. In the network the servers are in the addresses 192.168.1.122,
192.168.1.123 and 192.168.1.124.
An attacker is trying to find those servers but he cannot see them in his scanning. The command he is using is:
nmap 192.168.1.64/28.
Why he cannot see the servers?