If your antivirus is outdated and/or your subscription to virus definition updates has expired, do not make the mistake of thinking that as long as the antivirus product's icon is showing up in your system tray your computer is protected, nor should you lull yourself into thinking all is well because you scan your computer regularly with your outdated/expired antivirus.
Some people manage to convince themselves that they don't need an antivirus because they're "careful." They don't go to "bad" sites. They never open an e-mail attachment unless they know the person who sent it, and so on. Well, sorry... although those are all good practices, none of those things are enough to keep you safe without the use of a good antivirus. Every system needs an antivirus... an active antivirus. If you are running the same antivirus product that came with your three-year-old computer when it was brand new, and the subscription for virus definitions expired ages ago, you need to take action, NOW!
There are good paid antivirus products on the market and several free ones as well. I would advise that before you make your final selection you search the internet for reviews and opinions by everyday users of the various products. Paid ads are meaningless when making such selections.
You should also install a good antimalware product... one that can catch the things that an antivirus may not be designed to catch, such as spyware, adware, and various trojans. While a computer virus is malware that can copy itself and infect a computer without the permission or knowledge of the owner, trojans, just like the one in the Trojan War for which they are named, do not just come barging into your computer with a full frontal attack, they instead trick you into opening your gates and bringing them inside. Once inside, they do their dirty work.
New malware infections are discovered every hour of every day. Antivirus companies write "definitions" (like vaccine) for those infections as quickly as possible; however, it is understandably extremely difficult to create a definition to stop an infection that has not yet been created. Many antivirus developers try to do this to a certain degree by using heuristics, whereby the antivirus product looks for certain "earmarks" and, if found, may sound an alert and/or quarantine the suspicious file. It is not advisable to make these heuristics overly sensitive, lest they begin to erroneously identify good files as bad files.
It is important that we do not regard our antivirus and/or antimalware products as bullet-proof protection against any and all malware, as that only serves to give us a false feeling of security and makes us much more vulnerable to malware attacks. There is no antivirus, nor security suite, nor antimalware product that can protect us against the biggest danger faced by any computer... the person sitting in front of the keyboard. We must, therefore, be ever vigilant.
If you have a preference for a particular antivirus product, then use that one. Personally, I like an antivirus that is not bloated and has a small "footprint." If an antivirus slows my computer down, or is too intrusive, then that one is not for me. Use the one you like, but whichever one you choose, no matter how good it is, it will immediately become useless if its definitions are not kept up to date, so the subscription must never be allowed to elapse.
Surf safely.
