Understanding how Anivirus works

Hello,

Here's 2 scenarios I encountered:

1-
Installed an Antivirus on a PC;
One month later (scheduled), I scanned, found a good number of detections/infections, then cleaned them.

My questions are:
a- Shouldn't the installed Antivirus prevent viruses from getting onto the PC? or an Antivirus function is just to detect them after scanning?
b- If the Antivirus function is to prevent, should I drop that Antivirus?

2-
There is only one Antivirus that I know that scans fully removable devices (flash memory, external HD) before giving the possibility to open them; others try to detect, clean but give the possibility to open them which put the PC at risk; therefore, I ask people not to open the removable device, go to My Computer, right click on the removable device and scan it before opening it (which most peole forget to do)

My question is:
a- Will I go for such an antivirus that fully scan the removable device before giving the possibility to open them?

Thank you a lot,

1-
Installed an Antivirus on a PC;
One month later (scheduled), I scanned, found a good number of detections/infections, then cleaned them.

My questions are:
a- Shouldn't the installed Antivirus prevent viruses from getting onto the PC? or an Antivirus function is just to detect them after scanning?
b- If the Antivirus function is to prevent, should I drop that Antivirus?


1a. Doesn't sound like you scanned your PC immediately after installing the AV. If that's the case, how do you know the infections weren't already on the machine prior to the first scheduled scan?
1b. Yes an AV should prevent things from infecting your machine. But no antivirus, antispyware, antiwhatever is going to be 100% effective 100% of the time. If there was such a product we'd all be using it and every other company would be out of business. That's why on-demand scanners are recommended to supplement the primary real-time antimalware installed on a machine. Some of the more popular (in to particular order) are Malwarebytes, ESET Online Scanner, Superantispyware, Hitman Pro, Trend Micro HouseCall, Windows Defender Offline, Norton Power Eraser, etc.

2-
There is only one Antivirus that I know that scans fully removable devices (flash memory, external HD) before giving the possibility to open them; others try to detect, clean but give the possibility to open them which put the PC at risk; therefore, I ask people not to open the removable device, go to My Computer, right click on the removable device and scan it before opening it (which most peole forget to do)

My question is:
a- Will I go for such an antivirus that fully scan the removable device before giving the possibility to open them?

I haven't tried all available antivirus programs so I'm not sure what features that have or don't have. I'm currently using Microsoft Security Essentials and Malwarebytes. The both provide a right-click option to scan external hard drives, flash drives, files, folders, etc before opening them. I'm guessing that other reputable antivirus products will have the same option to right click and scan. You just have to try and find. (Most products offer a free trial so consumers can make educated decisions about the various products.)

Hi marsmimar and thank you for your reply.

In fact, I installed the Antivirus after a full format and Windows Installation. I did the scan one month later, found the viruses and cleaned them.

To tell you the truth, I've been using Avira free and Avast free for the last couple of years after using almost all existing antiviruses and I haven't really seen any difference between all antiviruses, but now, i am hesitating to continue using free security solutions since in my region (I live now in the Middle East) people tend to believe that paid (expensive) things, in this case antivirus solutions are much better.. therefore I am taking the decision to go for paid antiviruses, which takes me to the dilemma of which to use.

Here, people are more acquainted to Norton, Kaspersky and Nod32.. I am tending to go for Nod32 or kaspersky since the latter scan removable devices fully when plugged.

Nothing wrong with Norton, Kaspersky, or Nod32. They've all been around for a while and have good reputations. In fact, depending on which antivirus review forum you look, they've all been rated "best" at one time or another. So my only suggestion is try to get a free 30 day trial, use each one, and see which one you like best.

One caution: make sure you completely uninstall one product before you install another. That might require you to use an official uninstaller made by teh company itself - not just using control panel > programs and features. Here's a list of product uninstallers as provided by Microsoft. Each vendor may change the uninstaller at any time so it's always a good idea to check the vendor's website and search for "uninstall tool".

List of anti-malware product removal tools - Microsoft Answers

A/Vs are the last line of defense, not the first. Sandboxie is your friend.