AVG - this is an antivirus program you can use if you don't have the money to buy an antivirus software program. Its limited but it will get the job done. My only pet pieve is a while back I tried to install another antivirus software and it would not come off the system. Luckily they do have a program on the avg site which is a removal utility.
Malwarebytes - when it comes to antivirus software most antivirus programs can't catch them all. This software is able to detect those virus programs that are hard to take off. Well most of them. Free to use the removal tool although not a complete antivirus program since this only removes malware.
My best recommendation is do get a paid antivirus software if possible.