A JW from Malaysia once told me that were they to even attempt to witness to just one Muslim person, the JWs would be banned from that country.
Instead, the Malaysian JWs focus on the Buddhist, Hindu and Christian elements of the population. And, as others here have correctly guessed, most of the "converts" have come from the Christian population.
(The majority of Malaysia's population is made up of the indigenous Malays, who are Muslim by religion. Chinese make up a large minority, most of whom are Buddhists. The other principal group are those whose ancestors came from what was then British India - the modern day countries of India, Pakistan, Sri Lanka and Bangladesh. Their religions are Hinduism, Islam - and to a lesser extent, Christianity).