Antivirus

I really need one?

The antivirus are programs to protect your pc from viruses and trojans, If your pc have internet access is recommended have an antivirus, but is not install and that's all, no, you need update almost once a week(I really recommend try to update each day)

Which is the best antivirus?

It depends of what you need, for example Norton antivirus is really good, but in old pcs it makes slower, for old computers or slower computers I recommend you Symantec Antivirus Corporate Edition. But Mcafee and Trend Micro are good too. All depends of your internet usage and how much you want to spend for the antivirus.