Remember that you should never run two or more firewall products side-by-side. If you plan to switch to one of the products below, ensure that you disable Windows Firewall and any other firewall you have installed first.
Windows Firewall "is a common choice since it passes all inbound tests (both stealth and open port) and doesn't have many popup alerts. It doesn't require installation, so it's not likely to conflict with your other programs. And many average users wouldn't reliably handle the popup alerts of the best firewalls on the market (especially at their max settings)." (Best Free Firewall)
Access has to be defined for each application using one of four modes; out only, in only, enable all, or disable all. I suspect for many this will not offer a fine enough degree of control.
Comodo Firewall "is the best choice for users seeking a full featured security suite. This latest release is suitable for both lightly-skilled users (still must have knowledge of installed programs) and technically advanced users. Its robust and active HIPS (or application monitoring feature), called "Defense+", matches or exceeds the security performance of pay products. Comodo allows for much control and customization for the curious or the paranoid." (Best Free Firewall)
I recommend that you read our guide, How to Install Comodo, before you install it. Comodo Firewall is one half of Comodo Internet Security which is what you are actually installing. It also includes the other half, the anti-virus component which provides Defense+ (HIPS) and Sandboxing. But you can opt of of installing Geek Buddy (22 MB) by selecting the "Customize Installer" option.
The boundaries have blurred between security products so I have chosen to include all products in this category except for those that focus on removing malware which are in the next category.
Many of the applications are hybrid 64-bit applications where only the low level kernel mode drivers that interface with operating system are written in 64-bit code.
You can have more than one product installed, but you can have problems if you have more than one product enabled for real-time scanning. The same applies to email scanning.
MSSE or MSE has "great detection rates, particularly for rootkits. Even more impressive is that Microsoft Security Essentials has very few false positives, is light on resources and is good at removal of existing malware.MSE is a great choice for average users because of the minimal user interaction required. It automatically updates and removes threats. … The main downsides are the slow scan speeds and the lengthy amount of time it takes to quarantine malware, though in my opinion these are rather trivial concerns". (Best Free Antivirus Software)
Avira Antivir was formerly the Top Pick in its category. "AntiVir is still a top notch antivirus scanner with outstanding detection rates of malware, higher than almost every other antivirus according to tests. AntiVir is still a good choice for a free antivirus scanner, particularly for high risk users. However, there are some minor reservations. First, AntiVir does not include web or e-mail scanning capabilities … it just means that AntiVir won't warn you of infected emails before you open them. … Also, AntiVir contains a rather intrusive advertisement every time it updates." (Best Free Antivirus Software)
Avast! Free Antivirus "has steadily been improving its detection rates over the past few years and now ranks with the some of the best.Avast has the most features of all the free antivirus with full real-time capabilities including web, e-mail, IM, P2P and network shields, boot-time scanning, and a behavioural blocker … an internet site ratings plugin, script malware protection and a limited (non-configurable) sandboxing feature. …Lastly Avast is also light on resources." (Best Free Antivirus Software)
Many of the protection mechanisms used by Avast rely on interactive Windows services. Support in Windows 7 and Vista 64 for interactive services is intended for use by legacy applications. This places restrictions on the information that can be sent to the user.
SUPERAntiSpyware (SAS) free version "does not support real-time blocking, scheduled scanning and some other features." but it is a very good on-demand scanner which won't conflict with real-time protection. "In addition to its focus on detecting and removing spyware infections, this program deals with trojans and other types of threats such as diallers, keyloggers, worms, rootkits, etc." (Best Free Trojan Scanner and Remover; also Best Free Adware-Spyware-Scumware Remover),
"The interface is simple, updates are speedy but it still installs a start-up item which doesn't actually do anything at all. The scan speed is twice to thrice that of Malwarebytes Anti-Malware and the detection is less than half of it. The removal also left a lot to be desired". (Best Free Adware/Spyware/Scumware Remover)
Malwarebytes Anti-Malware (MBAM) "is an on-demand scanner which can be used to find and remove trojans, along with other malware such as viruses, worms, rootkits, diallers and spyware. While it will never win any prizes for its user interface, the program is intuitive and simple to use. … Other features include: multiple-drive scanning; quick scanning; ignore list; quarantine, to hold threats prior to deletion or restoration; along with various settings to enhance performance of the program. FileASSASSIN is also included to enable deletion of locked files. Another plus point is MBAM rarely causes any conflicts with other anti-malware utilities. (Best Free Trojan Scanner and Remover)
"The interface is very simple, … The scans are very fast and detection is first class." (Best Free Adware/Spyware/Scumware Remover)
I have separated specialist on-demand scanners from the other products which all provide on-demand scans as well. The free products listed here are more likely to be portable scanners. Portable so they can be used in a hurry and run from a disk or USB stick to check an infected system. Free so you can detect a problem but not free to remove it. Although they usually have an option to trial the removal component before having to buy the full-version.
The scanners listed here use a range of scanning technologies which can improve your detection rates if you use all of them: cloud-based (usually require a broadband internet connection to be useful), behavioural, and signature-based.
Hitman Pro uses a cloud-based scanner that has free detection. The removal option is only free for 30 days but that 30-day period doesn't start with the first scan, it starts when you first repair your system. You can install it or leave it portable. When installed, it can be configured it to run a daily scan. The scan runs very fast. Hitman Pro identifies files that need to be checked then uploads them to Cloud Scan where five scanners are used from IKARUS, PrevX, G Data, Emsisoft and Dr. Web. On my system it only uploaded a few files for scanning. Later scans were even faster because no new files were identified. Hitman Pro can also identify tracking cookies for deletion. ('gets a quick mention' in Best Free Anti-virus Software)
Emsisoft Anti-Malware free version provides a 30-day free trial of the full version which then downgrades to a freeware scanner and 'does not provide other features such as file guard, behavior blocker and surf protection'. The scanner is signature-based so when it runs it will download the latest signatures. There are four scan types: Quick (it is), Smart (much slower as it scans all programs), Deep (very slow scanning all files) and Custom. (Top Pick in Best Free Trojan Scanner and Removeralso 'gets a quick mention' in Best Free Antivirus Software)
A portable version of SUPERAntiSpyware which is reviewed above. It has four scan types: Quick, Critical Point, Complete, and Custom. The Custom scan appears to be the most flexible of any of these products. The Rescue Scan feature allows SAS to 'rescue' CPU cycles from malware hogging the processor.
Trend Micro HouseCall is an installer that doesn't openly install its malware scanner - it stores it in your user appdata\local\temp folder. So it may look portable but it isn't. It has three scan types: Quick, Full and Custom. Because it is so slow I would choose a faster scanner to initially detect suspected infections. There are positive reports of HouseCall having excellent detection. On the other hand there are reports of malware halting HouseCall's download and I've experienced the old problem with the scan stopping while "listing processes". As Trend Micro do not openly support their software this is a significant negative.