Abstract
Credit card fraud detection faces a dual challenge: severe class imbalance (fraud rates?0.2%) and strict privacy regulations preventing cross-institutional data sharing. Federated Learning (FL) allows multiple organizations to work together to train a common model while maintaining privacy. To address this issue, this paper introduces the Federated Learning Synthetic Minority Oversampling Technique (FL-SMOTE), which provides security guarantees semi-honest adversary model to mitigate the aforementioned limitations. The key innovation lies in a hybrid encryption architecture that combines partially homomorphic encryption for secure nearest-neighbor ranking with the Cheon-Kim-Kim-Song (CKKS) scheme for encrypted sample synthesis and model training. Specifically, partially homomorphic encryption enables Euclidean distance summation, ciphertext comparison, and privacy-preserving ranking, while the CKKS encryption scheme is integrated into the VFL-SMOTE framework to secure both training and aggregation in FL. In addition, a quadratic term is included in the client’s loss function to mitigate the divergence between the local and accelerated global models. On two public datasets, FL-SMOTE achieves F1-scores of 0.825 (Credit Card Fraud) and 0.565 (German Credit), outperforming baseline VFL by 12.1% and 16.8% respectively. The encrypted model maintains comparable AUC (0.91 vs. 0.92 unencrypted), while reducing computational complexity by a factor of 53 compared to traditional Paillier encryption.
Subjects
- Engineering
- Mathematics and computing
Funding
The work was supported by the National Natural Science Foundation of China (62306108), Natural Science…
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THE BHI TRUST PONZI SCHEME (SOUTH AFRICA)
Date: Ongoing updates through February 2026 Perpetrator: Craig Warriner (Principal), with alleged co-conspirators
Case Description: The BHI Trust scandal remains one of South Africa’s most devastating financial crimes, involving the loss of between R1.9 billion and R3 billion. Craig Warriner, the “genius trader” behind the trust, turned himself in during late 2023, but the legal and recovery battles reached a fever pitch in 2025 and 2026. Warriner operated the trust as a textbook Ponzi scheme, utilizing “Old Boy” networks and high-profile brokers to lure in pensioners and high-net-worth individuals with promises of 20% annual returns.
In early 2025, the National Prosecuting Authority (NPA) faced heavy criticism for “provisionally withdrawing” charges against alleged co-conspirators Michael Haldane and Sona Pillay. However, civil recovery efforts by joint trustees have continued into 2026, aiming to claw back hundreds of millions in “fictitious profits” from early investors to redistribute to those who lost everything. The case is a masterclass in the failure of fiduciary duty; the FSCA eventually banned several advisors for up to 30 years for peddling the unlicensed scheme despite clear red flags, such as the lack of a website, the absence of regulated financial reports, and a fee structure that was triple the industry average.
Link to Original: Moneyweb – BHI Trust Scandal Deep Dive
