Improving malicious URL re-evaluation scheduling through an empirical study of malware download centers
Bibliographic record
Abstract
The retrieval and analysis of malicious content is an essential task for security researchers. At the same time, the distributors of malicious files deploy countermeasures to evade the scrutiny of security researchers. This paper investigates two techniques used by malware download centers: frequently updating the malicious payload, and blacklisting (i.e., refusing HTTP requests from researchers based on their IP). To this end, we sent HTTP requests to malware download centers over a period of four months. The requests are distributed across two pools of IPs, one exhibiting high volume research behaviour and another exhibiting semi-random, low volume behaviour. We identify several distinct update patterns, including sites that do not update the binary at all, sites that update the binary for each new client but then repeatedly serve a specific binary to the same client, sites that periodically update the binary with periods ranging from one hour to 84 days, and server-side polymorphic sites, that deliver new binaries for each HTTP request. From this classification we identify several guidelines for crawlers that re-query malware download centers looking for binary updates. We propose a scheduling algorithm that incorporates these guidelines, and perform a limited evaluation of the algorithm using the data we collected. We analyze our data for evidence of blacklisting and find strong evidence that a small minority of URLs blacklisted our high volume IPs, but for the majority of malicious URLs studied, there was no observable blacklisting response, despite issuing over over 1.5 million requests to 5001 different malware download centers.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.010 | 0.063 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.003 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".