Confidentiality is primarily improved by preventing unauthorized parties from viewing data while it travels across untrusted networks. A Virtual Private Network (VPN) addresses this by creating a protected tunnel between endpoints, commonly using tunneling technologies such as IPSec or TLS for secure communications.
The Study Guide explains the purpose of VPNs for remote access as: "A virtual private network (VPN) is a way to create a virtual network link across a public network that allows the endpoints to act as though they are on the same network." It also notes the practical security value of full-tunnel VPNs when traversing untrusted networks: "A full-tunnel VPN sends all network traffic through the VPN tunnel, keeping it secure as it goes to the remote trusted network... [and] is a great way to ensure that traffic sent through an untrusted network...
remains secure."
Why the other options are less correct for confidentiality: Firewalls control traffic flow but do not inherently encrypt remote communications end-to-end; extensive logging improves detection/forensics, not confidentiality; and IDS detects suspicious activity but doesn't prevent eavesdropping on the connection. For confidentiality of remote connections, VPNs (implemented with secure tunneling like TLS/IPSec) are the best answer.
References: Sybex CompTIA Security+ Study Guide (SY0-701) - VPN definition and role ; full-tunnel VPN guidance for securing traffic over untrusted networks .