As they admired Swedish handicrafts in a storefront window, one of their cell phones chirped with an anonymous note: "Try the blue sweaters. They keep you warm in the winter."
The tourist was "bluejacked"--surreptitiously surprised with a text message sent using a short-range wireless technology called Bluetooth.
As more people get Bluetooth-enabled cell phones--both sender and recipient need them for this to work--there is bound to be more mischievous messaging of the unsuspecting.
It's a growing fad, this fun with wireless.
Already, Web sites are offering tips on bluejacking, and collections of startled reactions are popping up on the Internet.
One site, www.bluejackq.com, was set up a British teenager.
"I bluejacked three or four people," said 13-year-old Ellie of Surrey, who runs the site and makes bluejacking a daily affair. "But one of them was particularly memorable. He was with his wife and I bluejacked him in a coffee shop. The look on his face!"
Using Bluetooth, which has a range of about 30 feet, she sent him a note asking how his coffee was and noting that she liked his wife's glasses.
Ellie said he looked and high and low and tried to figure out where the message came from, even sending text messages back and forth with his wife, but to no avail.
Bluetooth is fast becoming a standard on new cell phones, though Forrester Research says only 9 percent of phones in Europe currently feature it. The technology is also available in the United States.
The technology is handy for those who want to use wireless headsets with their phones or, for example, send data from the phones to Bluetooth-enabled printers. Wireless keyboards and computer mice also employ it.
In bluejacking, the provocateur takes advantage of a built-in feature in Bluetooth-capable phones that allows people to send each other their contact information.
On most phones, that service is switched on by default.
When Bluetooth is activated, it automatically seeks out other equipped handsets and sets up a link.
Bluetooth phones can be configured to block anonymous messaging, but people who carry them don't necessarily know that.
A bluejacker could even send someone a photo taken with a camera phone using Bluetooth. It doesn't cost a thing since the message isn't being routed through any phone company.
Ellie, whose parents asked that her last name not be used, likes how the Bluetooth messaging feature lets her buzz a large crowd of people. Everybody in range gets the message.
"In the E-mail field I always write 'You've been bluejacked by jellyellie," said Ellie.
She combs shopping malls with her friends, seeking recipients of unsuspected messages. But she has yet to be bluejacked herself.
"I'm still waiting for that day," she said. "That would be great!"