I never use my laptop without having antivirus software, and having it up to date.  One of my computers got a virus on it once and it took a couple of hundred dollars to get rid of it.  I don't want to fork out that kind of money again, so I use antivirus software.  I always make sure it's a good name brand of antivirus software, someone that has been around for many years and is trusted by the experts.  I had antivirus software on my computer at the time of the invasion, but the virus got through anyway.  I think it was because it was a free one that I had never heard of.  I know some of the free ones are really good, the ones that have been around for awhile.  I use a good free antivirus software now on my laptop and I scan it often.  It helps too that no kids play with my personal laptop.  Kids can inadvertently download something with a virus, causing a lot of problems.  I'm very careful with what I download onto my personal computer, and I use a good antivirus software to protect my laptop.