Since researcher Eric Butler released Firesheep on Sunday, the add-on has been downloaded nearly 220,000 times.
"I was in a Peet's Coffee today, and someone was using Firesheep," said Andrew Storms, director of security operations at San Francisco-based nCircle Security. "There were only 10 people in there, and one was using it!"
But users aren't defenseless, Storms and several other experts maintained.
One way they can protect themselves against rogue Firesheep users, experts said on Tuesday, is to avoid public Wi-Fi networks that aren't encrypted and available only with a password.
However, Ian Gallagher, a senior security engineer with Security Innovation, argued that tosses out the baby with the bathwater. Gallagher is one of the two researchers who debuted Firesheep last weekend at a San Diego conference.