Hi there! Thanks for taking the time to write this. We assure you that Project Kat contains no viruses or malware.
As with any executable file on the internet, there's always a possibility of false negatives. A good way of telling if this is the case is checking virus total: Project Kat 64 bit and Project Kat 32 bit (v1.2.1) - As you can see there are 5 out of 66 anti-viruses that decided the 32 bit version may be dangerous (even though we compile both versions from the same code!), whereas zero did for the 64 bit version.
Anti-viruses tend to be overzealous about packed executables, especially unsigned ones. Ultimately it is up to you to decide whether to trust a random game you downloaded from the internet, but at least make sure you downloaded it from this page and not some sketchy site!