Let's face it: the Internet is a dangerous place.
In this case, I'm not referring to cyber crime, but cyber security. Even the best-informed can get into trouble with a single click. One bad file has the potential to turn a system into a useless paperweight. One could go out and spend considerable money on an Internet security suite, or piece together your own from the best free apps on the Web. In concert, the following five apps not only provide excellent virus/malware protection, but also keep your system running smoothly.
Avast! Free Antivirus
Like many anti-virus programs, Avast has had its ups and downs over the years, but it's currently one of the best free options out there. Boasting a Windows-8-style 'tile' interface, Avast! Free is comprised of a number of modules, or 'shields', to protect different aspects of your computer. These can be configured/disabled individually depending on the user's needs. Notable features include boot-time scan, real-time scan, virus chest, and audible warnings. Although completely free, the program must be re-registered every year by obtaining a free key from Avast.
In addition to the desktop version, Avast also offers a mobile security suite for Android.
Malwarebytes Anti-Malware
Malwarebytes is considered by many to be the best free anti-malware tool on the Web. It's known for being able to detect malware that others programs miss. The free version allows users to scan for and remove malware from a simple, no-frills interface. The paid version takes that step farther with real time protection, scheduled scans, and a flash memory scanner.
An Android app is also available.
Comodo Free Firewall
A firewall is a must-have for any computer with an Internet connection. At its core, a firewall prevents unauthorized parties from accessing a computer from an outside network, such as the Internet (or vice versa). Comodo may not be the best, but it's a solid option that's more than sufficient for the average user. In fact, Comodo's many personalized security alerts may get tiring after a while, but that's a small price to pay for system security. Originally part of a larger Internet security suite, Comodo Firewall can now be downloaded as a separate application.
IObit Smart Defrag
Although not strictly a 'security' application, IObit's Smart Defrag is a great alternative to the Windows Disk Defragmenter. It can help to speed up a system's file access by clumping together bits of data that are part of the same file, but strewn across the hard drive. Considered 'the world's fastest defragmenting engine', Smart Defrag can be setup to run in the background automatically (when a system is idle), at boot, or manually by the user.
Piriform CCleaner
From a security standpoint, CCleaner is a great utility for clearing browser history and Internet temp files, which can not only eat up large amounts of drive space, but also harbor infections. CCleaner can also remove unwanted registry keys, although this isn't recommended unless you're comfortable editing the registry.
DISCLAIMER: It goes without saying that these aren't the only options available. There are plenty of other pieces of free software that may do the job just as well or perhaps better. I'm not an expert in system security, and make no guarantees that this collection of programs will prevent all infections. However, if you're looking to bolster your defenses or are installing security software for the first time, I've had great success using these myself.
