Good security starts with developing the right mindset and applying a little personal effort, sadly there is no magic "app" that can take care of everything for you with a single click or tap.
Firewall, your first line of defence, without one you are a very easy target. If you are on broadband the router generally has a built in firewall and assuming it is active, they work very well but don't prevent applications going on-line, for this you need a properly set up software firewall on your PC. Apart from blocking incoming threats, good ones can stop programs automatically accessing the Internet without your consent, they will pop up and ask your permission. This helps by stopping some rogue software and trojans dialing home to infect your machine further or send out your data but you need to be pro-active.
Anti-virus protection, this is absolutely essential, this not only protects you but also your work colleagues, business contacts, family, and friends when you share files etc. If you use an email client such as Thunderbird or Outlook, most can scan your incoming emails as they arrive, this greatly reduces the chance of your machine becoming infected and the possibility of you sending a virus to your contacts. There are some decent free anti-virus products available but you will always get better protection from a paid for product. We highly recommend Eset, it is very reasonably priced, consumes a lot less system resources than most, can be customised, and the user interface is professional and polished.
Spyware and key loggers are a very real cause for concern, they can record your keystrokes when you are typing emails, letters, chatting, shopping on-line, banking etc, this collected information is then relayed back where it is scanned for any useful content i.e. credit card numbers, personal data.
Malware (malicious software) can damage your system and can also corrupt your data rendering it useless - backing up your documents, music, photos etc is not hard
Botnets, a botnet is a network of computers controlled remotely without the user's knowledge, these are used to spread malicious code, malware, and spam etc to others, your address book will often be harvested to increase the list of future victims. Your machine could become infected via email or web site visit and download links. People running botnets are part of a global network of highly organised professional cyber criminals who write and use very sophisticated software to steal from individuals and businesses. Their software is to be admired for it's effectiveness, tenacity and self repair ability.
Ransom-ware, can infect your machine and render it useless until you pay the people who infected your machine, you won't be able to use anything other than the shutdown button in the worst cases, programs will not launch - some ransom-ware removes all the menu items too, the Internet browser will open when you get into Windows and display a full screen page giving you the warning that you are infected and have to pay to remove the infection. Some come up with a page that looks like an official Police warning stating that you that you have accessed inappropriate / illegal content and need to pay. Ignore this, it is not from the Police or any other authority - do not under any circumstances pay them anything, instead get your machine cleaned up and install some decent anti-virus software.
Wannacry, we have listed this link as an example of ransomeware due to the havoc it caused world-wide, unlike past ransomeware infections, this one hit some major targets and made headline news: https://en.wikipedia.org/wiki/WannaCry_ransomware_attack
Software downloads, be wary downloading software from the Internet unless you know and trust the site. If you search for a particular product, you will often be presented with many download links, some official, others from large software repository sites. We have seen many instances of the downloaded software being wrapped inside another installer containing nuisance ad-ware, trackers, and unwanted browser toolbars. Don't blindly click on links without checking where they are taking you. If you want Firefox for example, search for who produces it and download directly from them, this approach does take a few more moments of your time but far less than cleaning your machine up.
Pirated software, ignoring the legal and moral aspects - just don't do it, this activity is mostly fraught with disaster. It is a fact that quite a few of these executable patches, cracks, and serial number generators contain malicious code that will infect your machine. You can instead search for a free alternative to whatever you require - there are plenty available!
The Metropolitan Police Service have a produced a few very informative pdf publications and they are available from their web site. They cover a lot of the scam techniques employed these days both on-line and off-line, they are: The little book of cyberscams, The little book of big scams, The little book of big scams business edition
The location of these pdf files changes regularly, here's a link to their web site search: https://www.met.police.uk/search/?q=book+of+scams
Get Safe Online - First class web site covering many of today's technologies and on-line activities with their potential security risks and safety implications.