Weird file auto-downloaded in Incognito, now clipboard shows random numbers—malware?

Unusual Chrome Incognito Incident: Unexpected File Download and Clipboard Anomalies — Is Your Device Compromised?

In today’s digital environment, cybersecurity vigilance is more crucial than ever, especially when encountering strange behaviors on your devices. Recently, a user reported encountering unusual activity after browsing on Chrome’s Incognito mode on a Chromebook, which raises important questions about potential malware infections or security breaches.

The Incident Overview

The user described an incident where, upon clicking a website link while using Incognito mode, their Chromebook immediately downloaded a file named stream.ts without any manual action. Recognizing the suspicious nature of this activity, they promptly deleted the file. However, the situation appeared to worsen the following day: after powering down for several hours, they noticed a peculiar change—an arbitrary number, such as 878442, sitting in their clipboard. This number appeared without any user initiation, and intriguingly, it kept changing every time they checked.

Potential Security Concerns

Such behavior—an unsolicited file download and random clipboard data—is often indicative of underlying malware or malicious scripts running in the background. Possible explanations include:

Malicious Scripts or Exploits: The initial download of stream.ts could have been a vector for malware delivery or a part of a malicious data exfiltration attempt.
Clipboard Hijacking: The random numbers appearing in the clipboard might suggest an attack that intercepts clipboard data to extract or manipulate information.
Browser or Extension Exploits: Even with extensions disabled or cache cleared, lingering vulnerabilities or malicious extensions could cause such anomalies.

Recommended Action Steps

If you encounter similar symptoms—unexpected file downloads, clipboard tampering, or unexplained device behavior—consider taking the following precautions:

Disconnect from the Internet: To prevent further potential data exfiltration or remote access.
Perform a Clean Reset (Powerwash): Chrome OS offers a factory reset option called Powerwash, which can remove persistent malware. Be sure to back up important data beforehand.
Review Installed Applications and Extensions: Temporarily disable all extensions and remove any unfamiliar or suspicious ones.
Scan for Malicious Software: Use reputable security tools compatible with Chrome OS or consult professional cybersecurity services if necessary.
Monitor for Recurrence: Keep an eye on clipboard activity and file downloads for any further anomalies.