  In recent years, blockchain technology has introduced decentralized finance
(DeFi) as an alternative to traditional financial systems. DeFi aims to create
a transparent and efficient financial ecosystem using smart contracts and
emerging decentralized applications. However, the growing popularity of DeFi
has made it a target for fraudulent activities, resulting in losses of billions
of dollars due to various types of frauds. To address these issues, researchers
have explored the potential of artificial intelligence (AI) approaches to
detect such fraudulent activities. Yet, there is a lack of a systematic survey
to organize and summarize those existing works and to identify the future
research opportunities. In this survey, we provide a systematic taxonomy of
various frauds in the DeFi ecosystem, categorized by the different stages of a
DeFi project's life cycle: project development, introduction, growth, maturity,
and decline. This taxonomy is based on our finding: many frauds have strong
correlations in the stage of the DeFi project. According to the taxonomy, we
review existing AI-powered detection methods, including statistical modeling,
natural language processing and other machine learning techniques, etc. We find
that fraud detection in different stages employs distinct types of methods and
observe the commendable performance of tree-based and graph-related models in
tackling fraud detection tasks. By analyzing the challenges and trends, we
present the findings to provide proactive suggestion and guide future research
in DeFi fraud detection. We believe that this survey is able to support
researchers, practitioners, and regulators in establishing a secure and
trustworthy DeFi ecosystem.
