This paper investigates the extent to which Open Source software is being adopted for web hosts within member countries of the Association of South East Asian Nations (ASEAN), and provides a partial explanation. We explain how Open Source software adoption decisions are influenced by macro-level or environmental influences (e.g. government policy, Open Source community). We use proxies based on empirical data collection to provide insight into the degree of Open Source software adoption which has already occurred. Software tools were developed to analyze web host software on the public Internet within each ASEAN country?s country-level domain. Other empirical indicators include Linux User Group (LUG) existence and activity. The study found that government Open Source policies do not appear to be a consistent factor among those ASEAN countries with the highest degree of Open Source software adoption. Other environmental factors appear to be more influential at this point in time.