Virus:   This is a special type of program that is able to infect itself into a computer without a users permission but requires a users intervention to spread.  A Virus is a program that attaches itself to  executable files and will cause an infection when a user runs the application that it was attached to.  Viruses range in complexity and scope to any of the following: some that just are minor annoyances to those that are so powerful to cause physical damage to computer hardware.

Infect: A term used by computer professionals to indicate that a file has installed itself into a computer,network or system without a users knowledge.  A common occurrence of this is when a user downloads a program and  it forces the system to shutdown, then carries out its installation instruction before the system is finished booting.

Trojan:  A special type of program which may appear to be functioning quite normally; however it is really acting maliciously behind the scenes.  This type of program will often get installed when you surf bad websites and our known to install back-doors into your computer and or network.   Once a Trojan is installed; your computer will allow the person that sent it to you, to illegally get into your computer.  A Trojan doesn't make copies of itself but it does do damage; because it opens up  your computer to be easily accessed, and taken over which  people call remote access Trojans.

Worm:  A worm on the other hand is a type of virus however; the way it infects is much different as its doesn't require user action.  For example one worm might send a copy of itself to everyone in your e-mail address book and then turn around and send itself to every one's book from each separate computer.  Worms have a unique property which is that they can easily copy themselves to files,folders,computer and other networks in your company, organization and eventually the entire Internet.  

Scanner:  A program designed to seek out viruses, Trojans, worms, identify them and then remove them.  It is also important to know that there are specific files that will target certain types; especially when they are free.  Many times people don't have a virus scanner, or have one but it won't remove anything because its just a scannerer and not a remover.. Most scanners are removers; however not all of them are and you can see exactly what a program will do by reading the help file and or the welcome screen when you execute the program 

Stinger Trojan Scanner 

Common Trojan /Backdoor Virus Removal Tools 

  Symantec Antivirus Removal Tool 

McAfee Antivirus Removal Tool 

Avast Antivirus RemovalTool 

Unfortunately Grisoft doesnt provide a separate uninstall utility but you can  download the link below then choose uninstall, reboot, then you can install the antivirus software of your choice.