The Feral-heart downloads from this website cannot give you viruses. (If you download FH from another source, there's no telling what you'll get.) What more likely happened was you've picked up a virus from another site, from downloading another program. Your security program might also be a bit weak or need updating. Even though Feral-heart itself will not give you viruses, make sure you run a complete scan before (and after) you download it, or any unfamiliar program, for that matter. If you don't have a strong security system, I suggest you find one as soon as possible. You can contract all kinds of bugs and malware without even knowing it, just by clicking/visiting websites (by the way, Feral-heart's website doesn't contain any viruses). If you had a security system on your mac but don't on your windows PC, now might be the time to install it. It's unlikely that Feral-heart has actually caused your computer issues, but more likely you've picked them up from elsewhere, and since installing Feral-heart, your computer is just now recognizing harmful bugs on your computer.
