Crypto-Islam

Crypto-Islam is the secret adherence to Islam while publicly professing to be of another faith; people who practice crypto-Islam are referred to as "crypto-Muslims." The word has mainly been used in reference to Spanish Muslims and Sicilian Muslims during the Inquisition (i.e., the Moriscos and Saraceni and their usage of Aljamiado). With the Portuguese Empire's expansion to the Far East and the Spanish Empire's spread to the Philippines from Latin America, Filipino Muslims and Portuguese Muslims were also subject to the Inquisition, one famous case being Alexo de Castro of the Spanish-occupied Moluccas, who was tried for crypto-Islam a continent away before the Mexican Inquisition.

Historic examples
Some historical examples include Ahmad ibn Qasim Al-Hajarī, 16th-century crypto-Muslim from Spain who authored a book recounting how he organized his escape from Spain to Morocco, and including a refutation of Catholic opinions about Jesus. The books also included details on crypto-Muslim life in Spain. He later became Ambassador of Morocco to Spain.

The Oran fatwa issued in the context of the persecution of Muslims in Spain gave guidance to crypto-Muslims on how to balance religious obligations with concealing their faith, allowing relaxation of sharia obligations in certain situations.

In 16th- to late 18th-century Russia, the native Muslims of the region faced frequent persecution by the authorities, which saw many episodes of forced conversions to Christianity. During these times, the newly converted continued to secretly practice Islam. Once Russia allowed Muslims to practice their faith, many of the converted reverted to Islam.