A malware sample that checks for internet access can look inactive in a disconnected sandbox. In his analysis published August 25, 2025, Khalif AL Mahmud reports that an isolated Windows 10 virtual machine, connected to simulated network services, exposed FlexenseActivator.exe’s connectivity check and later activity. The findings describe one sample and one lab setup—not behavior independently reproduced here or a profile of every Tiggre/Zpevdo file.
Why the sample needed a simulated network
AL Mahmud identifies the file as FlexenseActivator.exe, attributes it to Trojan.Win32.Tiggre / Zpevdo, and says it was distributed in pirated Flexense software archives. Its reported SHA-256 is 18676ae2eaa48ac6037fa239d282acca0b6c7cd6c7d384abe6b5cd379f2c5e50. That hash is a more specific way to identify the analyzed file than its filename: a different file with the same name is not necessarily the same sample.
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The analyst’s central problem was that a specimen expecting network connectivity may not proceed normally when it cannot reach a network. A disconnected environment can therefore hide behavior rather than prove the file is harmless. AL Mahmud describes using an isolated Windows 10 analysis VM connected to a REMnux gateway VM over a host-only network. INetSim simulated network services, while FakeDNS redirected DNS requests. According to his write-up and repository, the setup used isolated virtual machines and simulated services rather than live internet access; the repository contains analysis write-ups, hashes, and indicators of compromise, not malware binaries.
What changed when the lab answered the sample
AL Mahmud reports that the sample first checked Windows connectivity by requesting www.msftncsi.com/ncsi.txt, a Windows Network Connectivity Status Indicator (NCSI) endpoint. In his setup, the request received a simulated HTTP 200 response. The expanded account describes redirected DNS lookups followed by TLS connections used for certificate-chain checking. These observations support the idea that supplying a simulated response let this sample move beyond its connectivity check; they do not establish that every version or execution environment will behave the same way.
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| Analysis condition | What it can reveal | What it cannot establish |
|---|---|---|
| Disconnected sandbox | A sample’s behavior when network access is absent. In this case, connectivity-gated activity might remain unobserved. | That the sample has no network-dependent behavior or is benign simply because little happens. |
| Isolated sandbox with simulated services | In AL Mahmud’s reported setup, the NCSI request, simulated HTTP response, DNS redirection, and subsequent TLS activity. | How the sample would behave on a real network, or whether another configuration or sample would produce the same results. |
This is a comparison of two analytical conditions, not a controlled performance test. The benefit is visibility into behavior that depends on network replies; the boundary is that simulated services do not reproduce every property or response of the public internet.
Other activity reported in the analysis
Packing
AL Mahmud reports that the executable was UPX-packed and gives an entropy reading of 7.916. These are characteristics he observed in this sample, not proof by themselves of maliciousness or a universal trait of Tiggre/Zpevdo. Packing and high entropy are reasons to examine a file further, not verdicts.
GoogleUpdater-like files and process injection
The analysis describes GoogleUpdater-like directories and processes, then reports injection into five GoogleUpdater processes and into WMIADAP. The names and locations matter in context: familiar-looking updater labels alone do not establish legitimacy, and a process name alone does not establish compromise. The reported injection is a sample-specific finding, not a guaranteed behavior of other files bearing the same family label.
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AL Mahmud also describes suspicious cleanup activity, including unsigned executables re-executing from temporary locations. In an investigation, a sequence of file creation, process launch, and deletion can be more informative than any one event in isolation. The account does not make these behaviors conclusive indicators on their own.
What defenders can look for
The analysis suggests investigation leads, not standalone detection rules. Treat them as reasons to gather and correlate endpoint evidence:
- Repeated requests for
www.msftncsi.com/ncsi.txt, particularly when associated with an unusual executable or suspicious process lineage. - Multiple GoogleUpdater-like version directories or processes that do not fit the endpoint’s expected software and update history.
- Unusual process arguments, unexpected parent-child relationships, or evidence that a process is manipulating another process.
- Unsigned executables launching again from temporary locations, especially when combined with cleanup behavior.
- DNS or TLS activity that lines up in time with a suspicious process, rather than an isolated network event without context.
Correlate such observations with file hashes, signature status, process ancestry, timestamps, and other endpoint evidence before reaching a conclusion. A filename match is weak evidence; compare the file’s hash when determining whether it is the exact sample described here.
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How to read the detection figures
In his August 25, 2025 article, AL Mahmud reports a VirusTotal result of 33/76 antivirus vendors and a Hybrid Analysis score of 100/100. Those are figures reported in that article, not a current scan result or an independent measurement of prevalence. A separate Hybrid Analysis report for the sample is dated August 6, 2020, and shows a 55/100 threat score and 46% AV detection. The dates and report contexts differ, so these numbers should not be treated as a directly comparable trend or as a statement of present-day detection status. A historical sandbox report also cannot prove identical behavior across environments.
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The useful lesson is methodological: when a sample appears quiet without a network, connectivity may be a condition for further behavior. In this case, AL Mahmud reports that a host-only lab with simulated services exposed an NCSI check and later network activity, alongside packing, updater-like process activity, injection, and suspicious cleanup. These remain findings attributed to his analysis. The expanded write-up and repository are additional presentations of the same author’s work, not independent replications.
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The hash 18676ae2eaa48ac6037fa239d282acca0b6c7cd6c7d384abe6b5cd379f2c5e50 is the precise identifier supplied for the analyzed file; the name FlexenseActivator.exe alone is not. The case is a useful reason to avoid treating an inert run in a disconnected sandbox as a clean bill of health, while keeping conclusions tied to the evidence actually observed.
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