Ann, the network administrator, has learned from the helpdesk that employees are accessing the wireless network without entering their domain credentials upon connection. Once the connection is made,

A personal access point plugged in by an employee might cause similar connectivity issues, but it would not deliberately suppress credential prompts and is less consistent with a systematic pattern affecting multiple employees.

A DNS server attack would affect name resolution for already-connected users on the internal network - it would not cause the credential bypass or affect the wireless association process.

Compromised WEP encryption would allow an attacker to decrypt traffic or join the network, but it would not result in a separate open AP that bypasses credential prompts entirely.

An evil twin attack involves an attacker deploying a rogue access point that broadcasts the same SSID as the legitimate corporate network. Devices connect automatically or users connect without suspicion. The attacker controls the AP and does not enforce domain credential authentication, and since the AP has no path to internal resources, connected users get no internal access - matching both symptoms described.