Viruses suck. They are things you do not want on your computer. Giving them to other people is bad as well. HTG is a communication-intensive game. A virus scan should be performed on a regular basis, at least once a week, on your computer to help prevent passing on viruses to other players. Don't be fooled into thinking that you are always safe!
Of course, antivirus programs can't be expected to catch everything. It's a good idea to use multiple resources on a regular basis, and keep whatever program(s) that you use updated. The following programs are examples of free software that can be used to help protect your computer. It is just a small example, but these programs have proven successful.
Please note that HTG is not affiliated with any of these programs. If you have any questions or problems with them, you need to contact the authors. Don't forget to read the instructions/information on these sites before using the software.
Beware, you need to be aware that there are supposedly helpful software and sites that in fact far from helpful. Some infect your computer, others say they are removing spyware/trojans/viruses, but are really adding their own. Here are a few online antivirus programs to start with They are not meant to be a substitute for the full purchased programs by these companies, but are a good place to start.