Firstly, I should make it clear that the purpose of our Kollel is not to issue Halachic rulings. Any practical Halachic questions should be addressed to a competent local Rabbi. However I will attempt to show some sources relating to your question.

(1) The Rema in Shulchan Arukh Yoreh Deah 246:4 writes that a person should only learn Chumash, Mishnah, Talmud and the Halachic authorities that are based on the Talmud. This way he will acquire this World and the World to Come, whilst he will not acquire this through the study of other wisdoms. Rema adds however that it is permitted to study other wisdoms, if one does not make a fixed study of them, as long as they are not Sifrei Minim - the books of heretics who do not accept Malchus Shamayim - the Kingdom of Heaven. Biur HaGra there #19 cites our Gemara Sanhedrin 100b as the source for the prohibition against Sifrei Minim.

(2) The Darkei Moshe Yoreh Deah 246:9 elaborates at greater length on the source for his own ruling in Rema. He cites Teshuvas Rivash #45 that books which attempt to cite proofs to uproot the words of the Torah, are certainly included in the category of Sifrei Minim mentioned by our Gemara. Rivash cites Rav Hai Gaon who writes that someone who leaves Mishnah and Talmud and occupies himself with other wisdoms will lose the responsibility of the words of Torsh and the fear of Heaven, and is wasting his time because he will remove from himself the words of Torah entirely. Rav Hai wrote that one can only find the fear of Heaven and the fear of sin, amongst people who spend their time learning Mishnah and Talmud.

(3) Rivash continues that one cannot prove anything from the Rambam's example in this matter because the Rambam first learnt the entire Talmud and only afterwards, in order to know how to answer the apikores, did he write the Guide for the Perplexed.

(4) The Chaye Adam 10:12 cites the ruling mentioned above in (1) that one is permitted to study other subjects apart from the Torah in a passing way, as long as they are not the books of apikorsim. I am not aware of a mention in the Mishneh Berurah to Sifrei Minim, because the Mishneh Berurah is a commenatry on the Orach Chaim section of Shulcahn Arukh, not the Yoreh Deah section, but there is something related in Shulcahn Arukh Orach Chaim 307:16 that one is not allowed to read lewd books, not only on Shabbat but also on weekdays because this is considered the "seat of the scornful" (see Tehilim 1:1).

(5) Rav Moshe Feinstein, zt'l, wrote in Igros Moshe Yoreh Deah 2:105 that one may not teach children in school from books whose authors deny the Torah. In 2:111 he writes that that books that deny Hash-m and books of idol worship are forbidden and in 2:137 that one must burn a Bible containing the commentary of missionaries.

Shavua Tov

Dovid Bloom