Travel review site TripAdvisor has acquired Where I’ve Been, a Facebook app build by an independent developer, for $3m (£1.5m) - the biggest deal yet for a Facebook widget.

The app lets Facebook users add a map of the world to their profile pages, to show which countries they have visited. More than 2.3m people have signed up for the widget.

The acquisition was originally reported by the Inside Facebook blog, though there doesn’t appear to have been any official confirmation of the story yet.

The widget was designed by Craig Ulliot, and has reportedly become the most popular travel app, with over a million more users than Cities I’ve Visited, another app owned by TripAdvisor.

Since the opening up of the Facebook platform, a huge market has developed for widgets designed for the site. They offer a way to reach the social network’s estimated 55m users.

Slide.com recently acquired Favourite Peeps, a Facebook app with 1.3m users, for $60,000, which makes the reported price for Where I’ve Been look very expensive.

Further reading:

Launching a Facebook widget: dos and don’ts

Facebook widgets driving traffic to sites