The easiest way to play online games and install them from the internet is just to turn antivirus completely off when you're downloading, and while your playing. If you're downloading it, then only turn off antivirus if you trust it completely. If you think so but aren't completely sure, download the file and then scan it with antivirus. If you don't trust it, don't download it.
For playing the game, turning off antivirus will stop your antivirus/firewall from blocking FeralHeart's access to the internet.. again, if you don't trust it, don't turn off antivirus. Not only that, but most games run faster with Antivirus off, because when they're running the tend to make the computer slow down, which is more noticeable while you're playing a game. Honestly, I don't use antivirus all the time - I run a scan once a week, and I'm fine, but I'm pretty smart about what websites to go to and what to trust after being on it for so many years.
An easy way to tell what you can trust can be an extension in your web browser - for Chrome, I use "Ultimate Chrome Flag" which has pretty much every rating extension that exists rolled into one: It tells you where the website's server is from (IP Address, Country), their geographic location (City/Region), Google Page Rank (I don't use this part - I find PageRank to be useless), Alexa Rank (shows what rank it is among websites all over the web - For example, Google is Rank 1.. the FH forum is number 89134. Smaller number means more people go to it - so it's probably pretty trustworthy), Google Trends (shows how popular the website is over a period of months - it works best a year after the website is created, so it has a good amount of data - if it's going down, that could mean it's not safe, or it could just mean less people are interested), McAfee Advisor (if the page has been scanned it will find any viruses on the website), and Web of Trust. WOT is rated by normal people on four qualities of a website: Trustworthiness, Vendor Reliability, Privacy, and Child Safety. Obviously, for viruses, you'll probably want to look more at Trustworthiness and Privacy.. maybe Child Safety, but that depends.
If you have Firefox, there may be another extensions that's a lot like it - if you can't find it, just use WoT, since it's usually very good.