NEW YORK — It must have been easy for the terrorists, rampaging through Mumbai, to find the Chabad Jewish center where they slaughtered six people.

Signs in Hebrew and English are posted outside Chabad houses. The street address of each building can be found through the online global directory the movement developed to attract visitors. Worship and activity schedules at the centers are often just a few more clicks away.

But now the openness of the movement, always a strength, seems like a dangerous vulnerability. Chabad-Lubavitch leaders are struggling with how they can better protect their people without retreating from their mission to welcome and serve Jews worldwide.

"The challenge is it's a very open organization, a very transparent organization and an organization that has a tremendous and very effective outreach project," said Paul Goldenberg, national director of Secure Community Network, which oversees security for Jewish groups nationwide. "It's very tough for them to secure themselves."

Rabbi Zalman Shmotkin, a spokesman for the Brooklyn-based Chabad-Lubavitch, declined to discuss specifics of security for the 4,000 Chabad emissary families, or shlichim. The Web directory of Chabad locations in 73 countries remained posted after the Mumbai assault.

Sue Fishkoff, author of "The Rebbe's Army: Inside the World of Chabad-Lubavitch," said that in her travels overseas to research her book security measures weren't apparent at Chabad houses she visited, although she was aware that some safeguards were in place.

"I don't see how Chabad centers would be able to increase security and still fulfill their mission of being open and welcoming to anyone who steps inside," said Fishkoff, who writes for JTA, the Jewish news service.

The Secure Community Network, which was formed by the Conference of Presidents of Major American Jewish Organizations and other groups, does not include Chabad. Goldenberg said he plans to meet with movement leaders next week.

For decades, security has been a major focus for Jewish organizations because of terror attacks in Israel and on Jews elsewhere. The Anti-Defamation League, the Jewish civil rights group, distributes a security manual that runs for more than 130 pages, covering topics from armed intruders to bomb threats. As just one of their many precautions, the larger Jewish agencies don't publish their street address on their Web sites.

"Every terrorist starts with pre-surveillance and by gathering information on that target, and the place they start is the Internet," Goldenberg said.

But Chabad-Lubavitch wants its locations to stand out as they try to inspire Jews to become observant. On college campuses and in Chabad houses, couples who have dedicated their lives to the movement cook kosher dinners for Israeli backpackers and other Jewish travelers, teach rituals such as lighting Sabbath candles and lead classes on Judaism.

Like other staunchly traditional Jews, the men are easily identified by their long beards and black fedoras. Their wives cover their hair from public view and dress modestly, often in floor-length skirts. For religious and other reasons, they will not dress differently in public.

"I'm quite identifiable as a Jew and I'm happy and proud to walk around that way," said Rabbi Yosef Chaim Kantor, a Chabad emissary since 1992 in Bangkok, Thailand. "We are who we are."

Chabad began sending out emissaries in the 1950s, when the Lubavitcher rebbe, Menachem Mendel Schneerson, focused the movement on outreach to other Jews. Shmotkin said he knew of only one other case of emissaries dying in the line of duty, during a 1960s earthquake in Algiers.

Rabbi Gavriel Noach Holtzberg, 29, who was slain in the Mumbai Chabad house along with his 28-year-old wife, Rivkah, worked with Kantor as a rabbinic intern eight years ago in Thailand. Kantor, who oversees several Chabad institutions in the region, said the attack "does awaken a certain fear in some locations" but he said the movement will not restrict its work.

At a funeral for the Holtzbergs on Tuesday in Israel, Rabbi Moshe Kotlarsky, a Chabad official from New York, pledged to rebuild the Mumbai center and name it after the couple.

"We're trying to do as many positive things as possible," Kantor said in a phone interview. "We hope the moshiach (messiah) will come very soon and we'll all go to Israel and usher in a world of goodness and kindness and no more things like this. But until then, we have our work cut out for us."