Missing Malaysian Airlines Jet flew into area controlled by Taliban?

According to the Independent of the UK, one theory was that MH 380 may have flown under radar to Taliban-controlled bases on the border of Afghanisthan and North West Pakistan.

http://www.independent.co.uk/news/world/asia/missing-malaysia-airlines-flight-mh370-net-widens-as-pilots-passengers-engineers-and-crew-investigated-9195320.html

Sounds plausible.  But what does flying under the radar mean?

Further quote:

"For a commercial plane to pass undetected through these regions, which are highly militarised with robust air defence networks, many run by the US military, would require a combination of extremely sophisticated navigation, brazen audacity and security failure by those monitoring international airspace."

The mystery deepens!