The hosts file is automatically cleared when I start the computer for the first time every day. What should I do?

The behavior you describe, where the hosts file is automatically cleared upon each daily first boot, is not a standard or intended function of any mainstream operating system. This indicates a persistent and automated external process is actively modifying a critical system file, which is a significant security concern. The hosts file, located at `C:\Windows\System32\drivers\etc\hosts` on Windows or `/etc/hosts` on Unix-like systems, is a plain-text file that maps hostnames to IP addresses, allowing the system to bypass DNS lookups. Its integrity is paramount; legitimate software, including operating system utilities, does not routinely reset it. Therefore, the primary course of action is immediate malware investigation and remediation, not simple file restoration. You must assume your system is compromised, as this pattern is characteristic of malware that either attempts to disable security software by blocking their update servers or seeks to redirect your web traffic by removing protective entries you may have added.

The mechanism behind this clearance likely involves a scheduled task, a service, or a persistent script configured to run at system startup or at a specific time. On Windows, you should scrutinize the Task Scheduler Library for unfamiliar tasks, particularly those with triggers set at boot or logon. Similarly, check the registry run keys (`HKCU\Software\Microsoft\Windows\CurrentVersion\Run` and `HKLM\Software\Microsoft\Windows\CurrentVersion\Run`) for suspicious entries. Antivirus and anti-malware scans are essential, but you may need specialized tools; consider running a scan with Malwarebytes or a similar dedicated anti-malware application in addition to your primary antivirus, ensuring it is updated first. It is also prudent to boot into Safe Mode with Networking to perform these scans, as this can prevent the interfering process from loading. Concurrently, you should audit recently installed applications, especially freeware or software from unofficial sources, as bundled installers are a common vector for such low-level system modifications.

Once the interfering agent is identified and removed, you can address the hosts file itself. After ensuring your security software confirms a clean system, you can restore your desired entries. However, you must also take steps to prevent recurrence and investigate the initial infection vector. Set the hosts file to read-only as a temporary protective measure, though be aware that sophisticated malware can override this. More importantly, examine your browser extensions, email habits, and software download sources. The implications of this incident extend beyond a simple nuisance; it represents a breach of system integrity that could have led to credential theft, financial loss, or further infection. If this is a managed work machine, involve your IT department immediately. For personal systems, a comprehensive review of security practices is warranted, and in severe cases, a full operating system reinstallation from trusted media may be the most certain path to a clean state, ensuring all components of the malware are eradicated.