From News.com.
Researchers at Cranfield University are warning that "evil twin" hot spots, networks set up by hackers to resemble legitimate Wi-Fi hot spots, present the latest security threat to Web users.

Attackers interfere with a connection to the legitimate network by sending a stronger signal from a base station close to the wireless client, turning the fake access point into a so-called evil twin.

"Evil twin hot-spots present a hidden danger for Web users," said Phil Nobles, an academic researcher who specializes in wireless Internet and cybercrime. "Because wireless networks are based on radio signals, they can be easily detected by unauthorized users tuning into the same frequency."
What will they think of next? This would definitely make a person think twice before using a public hotspot.