What is the BLOWER file format?
A .blower file is a normal file, such as a document, photo or video, that has been encrypted by the Blower ransomware. Blower appeared in early February 2019 and belongs to the STOP/Djvu ransomware family. When it infects a computer, it scrambles files with the Salsa20 cipher and adds .blower to each name, so report.docx becomes report.docx.blower. Like other STOP/Djvu variants, it encrypts only the first 150 KB of each file, which leaves the tail of large files readable but still unusable.
Alongside the locked files, Blower drops a ransom note named _readme.txt. The note asks for $490 within the first 72 hours, rising to $980, and lists the contact addresses [email protected] and [email protected]. During encryption the malware often shows a fake Windows Update window and edits the Windows hosts file to block security websites. It usually spreads through cracked software, key generators, fake updaters and malicious email attachments.
Security & safety
RISK: HIGHA .blower file is the product of an active ransomware infection. Its presence means malware ran on the machine and may still be resident, re-encrypting new files or spreading. The file itself is encrypted data and cannot execute, but do not run the dropper or open _readme.txt links. Never pay the ransom or email the listed addresses. Isolate the machine, run a reputable antivirus, and attempt recovery only from clean media or the Emsisoft decryptor.
Format details
in a nutshellPrograms that open BLOWER files
Windows5 apps
Emsisoft STOP Djvu Decryptor
Free Run the decryptor to check whether your .blower files were locked with a recoverable offline key, then decrypt them back to their original form in place.
Malwarebytes
Freemium Scan and remove the active Blower ransomware and related malware before attempting any recovery, so files are not re-encrypted.
ShadowExplorer
Free Browse and restore earlier versions of files from Windows Volume Shadow Copies if the ransomware did not delete them.
Recuva
Freemium Attempt to recover deleted original files, since STOP/Djvu often encrypts a copy and removes the source.
Windows System Restore
Built-in Roll the system back to a restore point created before the infection, which may return some encrypted files to a clean state. Technical details
deep spec| Encoding | Salsa20 stream cipher; per-file key protected by RSA. Early STOP/Djvu variants such as .blower use an offline key when the command server is unreachable. |
| Byte order | N/A (original file bytes, partially enciphered) |
| Container | Original file wrapped in place; extension .blower appended to the full original name (e.g. photo.jpg.blower) |
| Compression | None added by the ransomware; original compression of the source file is preserved in the unencrypted tail |
| Encryption | Salsa20 for file contents, RSA for key protection. Only the first 150 KB of each file is encrypted, so large files retain a readable tail. |
| Typical size | Same as the original file plus a small appended block containing the encryption marker and key/ID |
| Structure | Original file header and first 150 KB enciphered with Salsa20; remainder of large files left intact; a marker and the encryption ID are appended at the end. |
| Integrity | None; no integrity field is added. |
| Platforms | Windows |
| Notes | Distributed through software cracks, key generators, fake updaters, bundled adware and malicious spam. During encryption it shows a fake Windows Update window and edits the Windows hosts file to block security sites. The ransom note _readme.txt is dropped in affected folders. |
| Released | 2019 (early February) |
| Specification | www.emsisoft.com |
BLOWER conversions
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