Rabbi Yosef Mizrachi (sometimes spelled: "Mizrahi") explains that it is permitted to lie to non-Orthodox Jews in order to trick them into becoming Orthodox and cites the Chazon Ish as proof. But to his credit, Mizrachi says we don't do this because it isn't our way. But it is indisputedly the way of Aish HaTorah, many Chabad shluchim, Ohr Somayach and many other haredi kiruv (outreach/missionary) groups.
I wrote about this concept before in FailedMessiah.com's distant past, but Mizrachi lays it out clearly. You can lie in order to trick a non-Orthodox person into becoming Orthodox because by becoming Orthodox and keeping the mitzvot (Divine commandments) you are saving that non-Orthodox Jew's soul.
We learn this, Mizrachi says, because it is required – he says "permitted," but the actual halakha, Orthodox Jewish law, is "required" – to break whatever Shabbat law necessary to save the life of another Jew, even if there is only a small chance of saving him or her and even if he or she will likely live only a few minutes more anyway. He also cites a ruling by the Chazon Ish (Rabbi Avrohom Yeshaya Karelitz, 1878-1953) who was the top Ashkenazi non-hasidic rabbi in Israel in the late 1940s through his death in 1953, who expressly said lies like this are permissible and even encouraged because saving a Jewish soul is greater than saving a Jewish life:
[Via: Jewish Outreach.]