Sensei blocking ns1.attdns.com .. ns2, ns3, ns4

[Sxg]

Why would sensei block requests to *.attdns.com under block category:web category and categorizes it as malware/virus.

[BNaCl]

Similar to IDS, it takes a bit of tuning to get the categories 100% for your environment. When you first turn on Sensei or make policy changes it is good practice to check to see what is being blocked via:

Sensei > Reports > Blocks > Live Blocked Sessions Explorer

Then add any necessary exceptions. Be careful not to whitelist entire categories which is the default. Just select the "hostname" radio button.