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Towards Making Systems Forget with Machine Unlearning

Open access
Cao, Yinzhi, Yang, Junfeng·2015·2015 IEEE Symposium on Security and Privacy

Abstract

Today's systems produce a rapidly exploding amount of data, and the data further derives more data, forming a complex data propagation network that we call the data's lineage. There are many reasons that users want systems to forget certain data including its lineage. From a privacy perspective, users who become concerned with new privacy risks of a system often want the system to forget their data and lineage. From a security perspective, if an attacker pollutes an anomaly detector by injecting manually crafted data into the training data set, the detector must forget the injected data to regain security. From a usability perspective, a user can remove noise and incorrect entries so that a recommendation engine gives useful recommendations. Therefore, we envision forgetting systems, capable of forgetting certain data and their lineages, completely and quickly. This paper focuses on making learning systems forget, the process of which we call machine unlearning, or simply unlearning. We present a general, efficient unlearning approach by transforming learning algorithms used by a system into a summation form. To forget a training data sample, our approach simply updates a small number of summations -- asymptotically faster than retraining from scratch. Our approach is general, because the summation form is from the statistical query learning in which many machine learning algorithms can be implemented. Our approach also applies to all stages of machine learning, including feature selection and modeling. Our evaluation, on four diverse learning systems and real-world workloads, shows that our approach is general, effective, fast, and easy to use.

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Crossref · 10.1109/sp.2015.35

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  • Cao et al.'s scheme has low applicability because only a few machine learning algorithms can be implemented as statistical query learning.

    “However, since the summation form comes from statistical query (SQ) learning, and only a few machine learning algorithms can be implemented as SQ learning, such as naïve bayes classifiers [83], support vector machines [84], and k-means clustering [85], this scheme has low applicability.”

    From Machine Unlearning: A Survey (2024) · cites this paper as [29]

    The Machine Unlearning section says many algorithms—including naïve Bayes classifiers, support vector machines, and k-means clustering—can be implemented as SQ learning and describes the approach as general. The Adaptive SQ Learning section says very few practical learning algorithms cannot be converted to its adaptive SQ form. These passages contradict the claim that only a few can be implemented and that this makes the scheme minimally applicable. (LLM, conf=0.92)

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  • The unlearning schemes proposed in References [29, 30, 33, 47, 68, 69] are essentially based on a retraining mechanism that naturally has a verifiability property.

    “The unlearning schemes proposed in References [29, 30, 33, 47, 68, 69] are essentially based on a retraining mechanism that naturally has a verifiability property.”

    From Machine Unlearning: A Survey (2024) · cites this paper as [29]

    The “B. Machine Unlearning” section explicitly describes the proposed approach as unlearning “without retraining from scratch”: it subtracts the forgotten data from stored summations and updates the model. The “C. Empirical Results” section compares unlearning with retraining to evaluate completeness, but that does not make retraining the mechanism on which the scheme is based. No page numbers are available in our copy. (LLM, conf=0.88)

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    Experimental — accuracy not yet measured
  • Because contexts are human-interpretable, ACE enables selective unlearning.

    “because contexts are humaninterpretable, ACE enables selective unlearning”

    From Agentic Context Engineering: Evolving Contexts for Self-Improving Language Models (2025) · cites this paper as Cao & Yang, 2015

    In “The Need for Systems to Forget” (page unavailable), the paper describes forgetting select data and letting users specify data to forget at different levels of granularity. That supports selective forgetting in general, but our copy does not identify ACE or say that human-interpretable contexts enable its selective unlearning. (LLM, conf=0.78)

    Experimental — accuracy not yet measured
  • Data replacement methods can reduce computational overheads and make unlearning operations more efficient.

    “Consequently, computational overheads are reduced, and unlearning operations are more efficient.”

    From Machine Unlearning: A Survey (2024) · cites this paper as [29]

    The Unlearning Work Flow section says the approach removes a sample’s contribution from stored summations and updates the model, making it faster than retraining. This supports the efficiency claim, but the paper does not describe the approach as a data replacement method. (LLM, conf=0.86)

    Experimental — accuracy not yet measured
  • The potential difficulty of removing memories that are tightly integrated into an LLM is demonstrated by the body of work done on 'machine unlearning'.

    “The potential difficulty of removing memories that are tightly integrated into an LLM is demonstrated by the body of work done on 'machine unlearning' [114]-[116], [124][126].”

    From Episodic Memory in AI Agents Poses Risks that Should be Studied and Mitigated (2025) · cites this paper as [124]

    Section B, “Machine Unlearning,” calls making learning systems forget one of the most difficult challenges and explains that complete forgetting requires reversing a training sample’s effects on learned features and models. The paper does not address LLMs or memories tightly integrated into them, so that application is an extrapolation. (LLM, conf=0.86)

    Experimental — accuracy not yet measured

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Cites

Flagged first, then by citations

2 of the 54 references couldn’t be matched to a known paper.

Research works printed but not linked: 3

  1. [27]27. Y. Cao, X. Pan, Y. Chen, and J. Zhuge. JShield: Towards real-time and vulnerability-based detection of polluted drive-by download attacks. In Proceedings of the 30th Annual Computer Security Applications Conference, ACSAC, 2014.
  2. [49]49. F. McSherry and I. Mironov. Differentially private recommender sys- tems: Building privacy into the netflix prize contenders. In Proceedings of the 15th ACM SIGKDD International Conference on Knowledge Discovery and Data Mining, KDD, 2009.
  3. [50]50. S. Muralidhar, W. Lloyd, S. Roy, C. Hill, E. Lin, W. Liu, S. Pan, S. Shankar, V. Sivakumar, L. Tang, and S. Kumar. F4: Facebook's warm blob storage system. In Proceedings of the 11th USENIX Conference on Operating Systems Design and Implementation, OSDI, 2014.

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Authors
Cao, Y., & Yang, J.
Affiliations
Columbia University (US)
Venue
2015 IEEE Symposium on Security and Privacy
Publisher
IEEE
Published
2015-05
Pages
463-480
ISSN
1081-6011 (ISSN-L)
OpenAlex
W1488996941
Cited by
622
References
54
Citations by year
2026: 135 · 2025: 165 · 2024: 116 · 2023: 66 · 2022: 37 · 2021: 48 · 2020: 20 · 2019: 13 · 2018: 9 · 2017: 9 · 2016: 4
FWCI
4.13
Type
conference paper
Language
en
Open access
Locations
IEEE Symposium on Security and Privacy (S&P) (publishedVersion)
Funders
  • National Science Foundation (1054906, 1162021, FA8750-10-2-0253, FA8650-11-C-7190)
  • Office of Naval Research (N00014-12-1-0166, N00014-12-1, N00014)
  • Air Force Office of Scientific Research
  • Air Force Research Laboratory
Topics
  • Physical Sciences › Computer Science › Artificial Intelligence › Privacy-Preserving Technologies in Data
  • Social Sciences › Sociology and Political Science › Privacy, Security, and Data Protection
  • Physical Sciences › Computer Science › Information Systems › Cloud Data Security Solutions
Keywords
machine unlearning, data lineage, privacy, anomaly detection, data poisoning, feature selection, recommender systems, data propagation

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