The official collection is reasonably priced ($24.99 USD on Steam) and often goes on sale for $19.99. You get cloud saves, achievements, and no virus risk.

If you have downloaded a legitimate (or preservation-based) copy of this archive, you should expect four main titles:

A downloadable compilation ("Castlevania: Dominus Collection") that packages multiple Castlevania-style levels, assets, and optional tools (level editor, soundtrack, README) into a single .rar archive for distribution. Designed for a fan-made, noncommercial release.