Let me answer your question about needing anti-virus (AV) software. (I can provide links to articles to back up what I’ve said here on request.)
The overwhelming number of Macintosh users go without. Yet you never hear of an entire office that uses Macs being ravaged by malware. And if you are on a Macintosh discussion list you never hear from any users whose Macs were damaged by malware. That’s because there are extremely few threats in the wild for the Macintosh (there are *a huge number* for Windows), and because the Macintosh has several layers of malware protection built-in.
There is also a reason to avoid anti-virus software. That is that a lot of AV software does more harm than it prevents. Most fully interactive AV software has been known to slow Macs to a crawl, and some AV software from certain vendors has been known to carry malware itself, or to do malware-like things.
I know that some folks want anti-virus software, even after being told that they don't need it. So here is a product that is known to be both effective, and harmless to your Mac. The good news is the best AV software for your Mac (based on the last believeable comparison tests from a few years ago) comes in a free version!
VirusBarrier Free Edition (free)
Intego Launches VirusBarrier Scanner — Free Mac Antivirus | The Mac Security Blog
Intego VirusBarrier Scanner on the Mac App Store
This is a full version of Intego's anti-virus program VirusBarrier [usually $40/year] minus some [but not all] of the automated scanning features in the commercial version. For those who don't know, Intego's VirusBarrier is the only anti-virus [AV] program that comes from a company that only creates software for the Macintosh. And that company is extremely effective at discovering new malware as it comes on the scene and updating their product to protect against it.
Have a look at this respected review site:
The Safe Mac » Mac anti-virus testing 2014
(Scroll down to the table listing various product’s efficacy.)
Macworld:
"Intego’s Mac Internet Security X9 [includes VirusBarrier] is our pick of the bunch, making it the best antivirus."
Intego Mac Internet Security X9 Review - Macworld UK
(Note that there is a more recent comparison test of AV software by Macworld on the Web. However, I haven’t found their tests credible since they discontinued their print publication and fired all of their staff.)
(I’ve been using the commercial version of VirusBarrier for 19 years now. It might make you feel good to know that the program has never “saved” me from anything that I really needed saving from in all that time. It has flagged things like phishing e-mails [which are easy to spot on your own], and Windows viruses that show up via e-mail [which are also easy to spot on your own, and which can’t run on the Macintosh]. So I really could have done without it just fine.)
If nothing else, the value in having this free AV program is that if you are the paranoid type, you can now use the best program available to satisfy yourself that you aren't infected with something. Also, this free version is sandboxed and it isn't deeply embedded in your system, like other AV programs, so it shouldn't impact your Mac's overall performance as just about all the other fully interactive AV programs do.
Note that AV programs do little or nothing to combat adware. Adware isn’t malicious, it just serves up extremely annoying ads. AV companies for some reason usually decide to ignore adware. So, in the event that you find yourself infected by adware, you may want to download and use:
DetectX Swift
DetectX – sqwarq | security for your mac
or
Malwarebytes
https://www.malwarebytes.com/
Both of the above products purport to be effective broad spectrum AV products. They are not. But they are excellent for dealing with adware. I prefer DetectX Swift because it is less intrusive than Malwarebytes.
One note. “Flash” is a technology used by your browser to see some animated content on the Web. Flash has been sunsetted, but it is still really common on the Web, so you likely will want to have it installed and keep on using it for now. The problem is that fake pop-ups commonly exist on the Web that will offer to allow you to install or upgrade Flash, but if you click “yes” they instead will have you willingly downloading malware.
There are only two ways that you should EVER normally update Flash:
1) Via the Flash Player pane (under the Updates tab) in System Preferences on your Mac
or
2) Directly from Adobe:
http://get.adobe.com/flashplayer/
**YOU SHOULD NEVER UPDATE OR INSTALL FLASH FROM A POP-UP THAT APPEARS ON YOUR SCREEN**
If at any time you are wondering if you already have the latest version of Flash installed, you can check in the Flash preferences pane, or you can find out which version of Flash you currently have installed, and what the latest version is, here:
http://www.adobe.com/software/flash/about/
Good luck!