More than a dozen people have been arrested by Indonesian anti-terrorism police, authorities said Monday, as they beef up security in the world’s biggest Muslim-majority country ahead of the Christmas and New Year holidays. The Islamic State group (ISIS) now has a pervasive presence in Indonesia, the country’s military chief warned in June, where so-called “sleeper cells” are believed to have been established all over the Southeast Asian archipelago. Indonesia’s national police are closely watching 600 Indonesians who allegedly became foreign terrorist fighters and are affiliated with ISIS, according to Tempo.