RUENUpload file
Security

File security: scanning, protection, transfer

Files are the most common way problems get into a system. An infected installer, a tampered archive, a document leaked through an open link — it all starts with one carelessly opened file. This section of loadfile.ru is a practical guide to handling files safely: scanning downloads before you run them, understanding the risks of executable formats, encrypting important data, transferring it safely to other people, and not losing it in a failure. There is no theory for theory's sake here. Only what actually reduces the risk.

Start by scanning a file
File security: scanning, protection, transfer
!
The main rule

No file from the internet is safe “by default.” What makes it safe is a scan, not a source you trust. Even a file from someone you know can be infected — if that person's computer is infected.

Contents
  1. Why files are the main infection channel
  2. Scanning downloads for viruses
  3. Why EXE and APK are dangerous
  4. File encryption
  5. Safe file transfer
  6. Backups
  7. Where to start: a checklist
  8. Frequently asked questions

Why files are the main infection channel

Most infections start not with a hack, but with a user action: someone downloaded and opened a file. Malicious code is hidden in program installers, documents with macros, archives, shortcuts, scripts and even images with a double extension like photo.jpg.exe.

Three things determine how dangerous a file is:

  • File type. Executable formats (EXE, MSI, APK, BAT, SH, scripts) can run code. Documents (DOCX, XLSX, PDF) — through macros and vulnerabilities. Archives — as a container for everything above.
  • Source. The developer's official website and an app store are one thing. A file from a chat, a link from an email — another.
  • Your actions. You ran it with a double click, allowed macros, granted administrator rights — the risk became real.

Articles in this section

Cheat sheet · PDF

Dangerous extensions map: 60 formats

A reference of formats you must not open with a double click: exe, scr, bat, vbs, js, docm, iso, hta and others — why they are dangerous and what to do. Plus a printable cheat sheet for your team.

Open → Scanning

How to scan a file for viruses

Step by step about VirusTotal, Microsoft Defender, online scanners, checking the hash and digital signature, and the signs of an infected file.

Open → Risks

Why APK and EXE are dangerous

Infection vectors of executable files, how to spot a fake installer and where to get programs and apps safely.

Open → Transfer

Safe file transfer within a team

Cloud storage, S3/MinIO, self-hosted, encryption before sending, access control and versioning of large files.

Open →

Scanning downloads for viruses

Before running any downloaded file, it's worth scanning it. A minimal set of tools is available for free:

  • VirusTotal — an online service that runs a file through 60+ antivirus engines at once.
  • Built-in Microsoft Defender — right-click the file → “Scan with Microsoft Defender.”
  • Checking the hash and digital signature — to make sure the file has not been tampered with and was released by the stated developer.

Detailed guide: How to scan a file for viruses before running it

Why EXE and APK are dangerous

Executable files are programs. By running an .exe on Windows or installing an .apk on Android from an unofficial source, you are essentially giving unknown code access to your device.

Typical risks: fake installers (a copy of a program with a miner/stealer); an APK outside Google Play (a trojan disguised as an app); requests for excessive permissions.

Detailed guide: Why APK and EXE from unofficial sources are dangerous

File encryption

Encryption protects data even if a file ends up in the wrong hands: a stolen laptop, a lost flash drive, an intercepted transfer. Without the key, an encrypted file is a useless set of bytes.

ToolWhat it encryptsPlatformPrice
7-Zip (AES-256)Individual files / archivesWindows, Linux, macOSFree
VeraCryptContainers and disksWindows, macOS, LinuxFree
BitLockerDisksWindows Pro/EnterprisePart of the OS
FileVaultDisksmacOSPart of the OS
💡
A strong password is essential

AES-256 won't save you if the password is 1234. Use a passphrase of 4+ random words or a password manager. Send the password through a channel separate from the file.

Safe file transfer

Transfer is the moment of greatest risk: the file leaves your control. The main principles: encrypt before sending; use links with restrictions (expiry, password, download limit); don't publish “forever” open links; control access.

Detailed guide: How to transfer large files safely within a team

Backups

Encryption protects against prying eyes, a backup protects against loss. Ransomware encrypts your files and demands a ransom; the only reliable defense is an up-to-date backup.

A working rule is 3-2-1: 3 copies of the data, on 2 different media, 1 of them — offsite (away from home/office).

!
A key detail

At least one copy should be offline or protected from overwriting (immutable storage). A backup that is always connected in write mode will be encrypted by ransomware along with the original.

Where to start: a checklist

  • ☐ Enabled automatic updates for the OS and antivirus.
  • ☐ I download programs only from official websites and stores.
  • ☐ I scan every downloaded file on VirusTotal before running it.
  • ☐ I don't open attachments and links from unexpected emails.
  • ☐ I encrypt important files (7-Zip / VeraCrypt) before storing and sending them.
  • ☐ I transfer files via links with a password and an expiry.
  • ☐ I make backups following the 3-2-1 rule, with one copy offline.

Frequently asked questions

Is the built-in Windows antivirus enough?

For most users — yes. Microsoft Defender shows results on par with paid antivirus products. The main thing is not to disable it and to keep the system updated.

Can you get infected just by downloading a file without opening it?

In the vast majority of cases — no. It's running the file that's dangerous. Exceptions are vulnerabilities in preview software. That's why it's better not to open an unscanned file.

Does an antivirus protect against ransomware?

Partly. The only guaranteed protection against ransomware is regular backups, at least one copy of which is not available for overwriting.

What should I do if I've already run a suspicious file?

Disconnect the device from the internet, run a full scan, change passwords from another “clean” device. If you have a backup — restore from it. In case of a serious infection — reinstall the system.

See also

File security is a set of habits, not a product

Scan before running, encrypt what's important, transfer with restrictions and always have a backup. Start with the most common scenario — scanning a downloaded file for viruses.

Go to file scanning