Trust no one. Trust not even your brother or sister, son or daughter, wife or husband, boyfriend or girlfriend, niece or nephew. H3ll, don't even trust your mom or dad when it comes to your in-game password. Only one person knows my password, and only SHALL one person knows; and that is MYSELF.
Make sure your password is not simple, and contain multiple characters. Do not have a password such as "hackme". Instead, create a more complicated password like 0mgUW1lLn3veRh@cKMyacc0uNt. Notice how I used numbers, lowercase and uppercase letters, and special characters, and how the password itself is long?
Have an antivirus or internet security install. Keep the virus database updated as much as possible. Stick with only 1 antivirus/ internet security. Scan your computer at least once a week. If you have a firewall, or is connected thru a router, turn on the firewall. Antivirus/Internet security softwares are not expensive. Most cost around $20-$60 depending on the manufacture (Symantec/Norton, McAffe, Avira, Avast, Bitdefender, nod32, AVG, etc) and stores. A lot of manufactures offer rebates, wherein after rebates the product is practically free. There are also some antivirus softwares that can be downloaded for free thru the net: AVG-free, Avira-free, Avast-free which contains less features and protection than their paid counterparts.
Stay away from downloading (you know what I mean) and torrenting, as they are known to carry trojans, rootkits, viruses, etc. Stay away from 18+sites too. If you must, use another computer that you do not play game on.