In the latest years, there has been a decline of both the historic religions of Bulgaria—Orthodox Christianity and Islam—, which shrank respectively from 86% in 1992 to 84% in 2001 to 61% in 2011 and from 13% in 1992 to 12% in 2001 to 8% in 2011. In the 2011 census, the question about the religious affiliation became optional, and thus 21.8% of the total population didn't answer.[1] Until the census of 1992, Bulgarians were obliged to declare the historic religious belonging of their parents and/or ancestors, while since 2001 people were allowed to declare personal belief in a religion or unbelief in any religion (irreligion and atheism).[3] After the end of the People's Republic of Bulgaria (1946–1990), the revival of Islam was stronger than Orthodox Christianity.[3] With the international rise of Islamic terrorism in the 2000s, however, there was a growing disaffection for the Islamic religion among Bulgarians.[3] The Bulgarian Orthodox Church has seen the most serious decline from 2001 onwards.[3] The church's credibility has been undermined since the 1990s by its collaboration with the erstwhile Communist regime,[4] fully revealed with the opening of the state's secret archives in 2012, according to which eighty percent of the clergy were members of the secret police.[5]