Selection of Virus softwares

Somehow Zemana Anti Malware got onboard.

I would be very concerned if software unexpectedly gets installed on my computer. Security Essentials is a good basic AV and even if you wanted something more powerful, I would not recommend Zemana

I agree with the above. You can also do a Full Scan with Malwarebytes as an added measure.

Remember to not open emails from strangers and to not click on enticing links.

Not much can stop invitations from you (any user)

Also top named (normally paid) Antivirus solutions are good.

Windows Defender on new versions of Windows 10 is excellent

Zemana is a perfectly functional anti-malware package and has the advantage of having a very small footprint on your PC .

I'd be more concerned that you missed its install. It's offered bundled with mainstream application upgrades as a deselectable option.  

There are many bundled software packages that are more of a risk to your computer and I'd suggest that you need to look at how you manage software installs as well as considering software to help protect it.

For example it sounds like your PC is running by default in an administrative account which can give anything that is launched unrestricted access to your system

I also agree software that some how appeared on your computer is not a safe way to go, it may be packaged with PUPS that you would not normally want or may be packaged with malware or viruses. I would definitely uninstall it. If you want to use the software download it from the antimalware website directly .

My only recommendations are based on 23+ years in the business professionally.  First, I recommend two types of protection, neither of them are free.  You get what you pay for.  Having spent a couple of years studying under some of the best minds in the malware fighting community, I base a lot of my decisions on that training and the various incidents uncovered during that time.   We trained with real malware and viruses.
    If you aren't using one of the top 5 antivirus softwares, you are very likely to be subject to a same day exploit.
   I don't give 2 hoots for any of the free stuff any longer, years ago, they were doing a great job of keeping up, now.... you need experts fighting to keep your system clean.
   As far as malware fighting, the only one that I put my money behind is Malwarebytes. They claim their endpoint solution is the end all beat all and that you don't need an antivirus.  The jury is still out on this, I'm suspect, and don't believe it yet.  But the premium version of Malwarebytes anti-malware is second to none.
  When it comes to antivirus I choose ESET Nod32 antivirus.  I do this because I've installed it on old and slow systems and new flashy systems as well and it causes the least amount of trouble and is priced comparably or a little less than the other top 4.

In response to Robert, taking into account the coverage and price I am going for Emisoft anti malware  , thank u for your inputs n regards.

Thanks for awarding me the points, although I do not have business dealings with them (by providing them referrals), I do find they are a reputable company with a good product.  They even have tools to remove various ransom viruses and can often get data back as well they have tools to remove malware on systems that will not boot to windows such as their emergency boot disc.  I am happy with their services.