There are many decent antivirus software on the market, pay special attention to Bitdefender, McAfee, BullGuard, Norton and Kaspersky. Please install official versions only, pirated software can cause serious damage to your OS and your reputation. Here's a great article revealing all the dangers and disadvantages of pirated software https://shareware.deals/pirated-software-and-why-you-should-avoid-it , take a look at it.