Five men believed to be responsible for spreading a notorious computer worm on Facebook and other social networks — and pocketing several million dollars from online schemes — are hiding in plain sight in St. Petersburg, Russia, according to investigators at Facebook and several independent computer security researchers.

The men live comfortable lives in St. Petersburg — and have frolicked on luxury vacations in places like Monte Carlo, Bali and, earlier this month, Turkey, according to photographs posted on social network sites — even though their identities have been known for years to Facebook, computer security investigators and law enforcement officials.

One member of the group, which is popularly known as the Koobface gang, has regularly broadcast the coordinates of its offices by checking in on Foursquare, a location-based social network, and posting the news to Twitter. Photographs on Foursquare also show other suspected members of the group working on Macs in a loftlike room that looks like offices used by tech start-ups in cities around the world.

Beginning in July 2008, the Koobface gang aimed at Web users with invitations to watch a funny or sexy video. Those curious enough to click the link got a message to update their computer’s Flash software, which begins the download of the Koobface malware. Victims’ computers are drafted into a “botnet,” or network of infected PCs, and are sent official-looking advertisements of fake antivirus software and their Web searches are also hijacked and the clicks delivered to unscrupulous marketers. The group made money from people who bought the bogus software and from unsuspecting advertisers.