It is extremely important to have one up-to-date security program on your computer. This will offer protection against viruses and other threats to the health and well-being of your computer, as well as the privacy of your information.
There are many security programs to choose from--some free and some paid with an annual subscription.
You should have only one security program on your computer at a time. Two security programs can conflict with each other and undermine your computer's security.
Below are links to a few mainstream security programs. AVG offers a free version of it's program, included below.
Note that anti-virus is the minimum level of protection you should have. If possible, opt instead for an internet security program, which provides more comprehensive coverage, but usually costs more. You will see both choices through the following links.