A file with a .crypt1 extension is a file that has been encrypted by the UltraCrypter virus, which is a variant of CryptXXX ransomware. It is encrypted so it is not possible to open the file by simply changing the file extension.

UltraCrypter is a type of malware utilized by cybercriminals that takes your files hostage and forces you to pay the perpetrator to unlock your files. It may be introduced to your computer through an executable file disguised as another type of file. This is typically done through malicious ads on compromised websites or email spam with attached files disguised as other files. When the ransomware runs on your computer, it encrypts and renames standard files that are important to you with a .crypt1 extension. The files are typically documents, images, videos, and backup files, such as .PDF, .JPG, and .DB files. For example, an example.jpg file becomes example.jpg.crypt1. The virus changes the desktop wallpaper then generates a .HTML ransom note informing you of the takeover and what you need to do to recover your files, which is typically a payment via Bitcoin. CRYPT1 files became prevalent in May 2016 and are similar to encrypted .CRYPT files. Currently, there is no program available to effectively restore your files. If you have a recent backup of your files, you can perform a system restore.