You paid the ransom, received the key, or downloaded a free decryption tool published by a security researcher, and your files are still unusable. This scenario is more common than most people assume. On complex formats like SQL databases or virtual machine files (VHDX, VMDK), decryption that leaves the internal structure corrupted is a typical outcome, not an isolated case: a documented bug in the Ryuk ransomware’s own decryptor, for instance, truncated large files (VHD/VHDX containers, Oracle and SQL Server databases) by a single byte — enough to make them unmountable despite the content being almost entirely decrypted. The data is technically decrypted at the binary level, but the file’s logical structure stays corrupted and the system refuses to start.
What actually happens during a ransomware attack
When ransomware hits a company server, it doesn’t stop at locking a handful of isolated files. It encrypts critical data at depth: SQL databases, virtual machine disks, archives, and production documents. Every file gets rewritten under an encryption algorithm, often within minutes for the heaviest volumes, which is why event logs typically show abnormal disk activity right before file extensions change.
Once the attack is over, a ransom note usually appears in several folders, with payment instructions and sometimes the promise of a working decryption tool once the sum is paid. This is the point where many companies believe they’ve found a quick fix. The reality of the restoration process is far less certain.
Why paying the ransom doesn’t guarantee full recovery
Obtaining a decryption key, whether by paying the ransom or through a tool released for free by a security researcher, never guarantees a full data restoration. Payment guarantees neither a genuinely working tool, nor a complete recovery, nor even that the same organization won’t be targeted again in the following months. On complex structured files, a partial decryption failure isn’t a rare, poorly documented exception: it’s a scenario recovery labs see on a regular basis.
Tools built under pressure, not tested in real-world conditions
The decryption tools attackers hand over after payment are built quickly, under pressure, with a single goal: proving that decryption is technically possible. They’re rarely engineered to handle edge cases cleanly: large files, fragmented formats, writes interrupted mid-encryption. The result is that they often work fine on simple files (office documents, images) but become unstable as soon as they run into more complex data structures.
The special case of databases and virtual machines
An SQL database isn’t a simple stream of data to decrypt block by block. It holds indexes, internal pages, and relationships between tables that all need to stay perfectly consistent for the database engine to read it back. The same applies to a VHDX or VMDK virtual machine file, whose header and allocation table must match the virtual disk’s contents exactly. A decryption tool that treats the file as a uniform binary blob, without respecting these internal structures, can leave nearly all of the content technically decrypted while leaving the database or VM completely unusable — a single byte misaligned in the header or allocation table is enough to make the file unreadable. Some ransomware crews do offer a form of technical support after payment, as part of a “reputation” strategy meant to keep future victims paying — but that support is entirely at their discretion, with no guarantee of results and no legal recourse if it fails to fix your case.
Decryption and data recovery: two different problems
This is the point most often misunderstood in this kind of situation. Decryption means recovering the plaintext content of an encrypted file: it’s a cryptographic problem. Data recovery means rebuilding a file structure that the system or application can actually use: it’s a problem of structure and integrity. A file can be perfectly decrypted in the cryptographic sense and still be unusable at the application level, because its headers, indexes, or internal tables were never put back into a consistent state during the operation. That’s exactly what happens to SQL databases and VM files after a poorly handled automated decryption.
What not to do after a partial or failed decryption
Faced with a disappointing result, the first instinct is often to run the tool again and again hoping for a better outcome, or to attempt a repair with generic SQL utilities found online. Both reflexes almost always make things worse.
- Don’t run the decryptor repeatedly on the same files: each additional pass can overwrite the last remaining usable structures.
- Don’t try to repair a damaged database yourself with a standard SQL repair tool: these tools assume ordinary corruption, not a structure altered by partial decryption, and risk deleting data that could still be recovered.
- Clone or back up the current state of the files before any further attempt, including the partially decrypted files: this is often the only usable copy left.
- Keep a copy of the original encrypted files and the key you obtained, in case a newer version of the decryption tool becomes necessary later on.
The professional approach to a failed decryption
Where an automated decryption tool stops, manual intervention at the binary and hexadecimal level can take over. This means analyzing the file’s structure directly: locating the SQL tables, VM headers, or indexes that were never properly put back into a consistent state, then rebuilding these elements one by one from what’s still usable in the partially decrypted file. This approach requires solid knowledge of the specific file format involved (the SQL engine in use, the VHDX or VMDK format version) and tools suited to this level of analysis, very different from consumer-grade repair utilities.
A lab specialized in server data recovery typically starts with a diagnostic to pinpoint exactly where the break lies between the data that’s technically decrypted and the logical structure the system expects. That diagnostic shows whether reconstruction is even possible before any further manipulation of the files, which avoids wasting time on an approach that wouldn’t have worked anyway.
Key takeaways
Getting hold of a decryption key, whether by paying a ransom or through a free tool, is only the first step. On complex files like databases and virtual machines, a partial decryption that leaves the internal structure corrupted is a frequent outcome, not an isolated accident. The right move isn’t to keep pushing the original tool or attempt a generic repair, but to preserve the current state of the files and bring in expertise capable of rebuilding the internal structures at the binary level. That step, distinct from decryption itself, is what determines whether your data becomes genuinely usable again.