From the moment you switch on your PC, your system faces countless Internet-borne dangers, including spyware attacks, viruses, Trojan horses, home-page hijackers, and hackers trying to weasel their way into your system. And the Internet isn't the only source of trouble. Anyone with access to your PC can invade your privacy by prying into which Web sites you visit--and learning a great deal more as well.

But fighting back is easy. We've found 15 great pieces of software--firewalls, spyware busters, antivirus software, rootkit killers, and general Internet security tools--designed to protect you against any dangers that come your way. They're free, they're powerful, and they're easy to use. So what are you waiting for? Start downloading.

Preventing and Eliminating Malware
From firewalls to antivirus software to tools for combatting rootkits and spyware, here are some great downloads that will protect your system against malicious attacks.

ZoneAlarm
Check Point Software's ZoneAlarm may well be the most popular free firewall on the planet, and the most recent release (finally) protects Vista machines. Arguably, ZoneAlarm is the product that made everyone conscious of the need for firewall protection. It's extremely easy to use, and its method of configuring outbound protection is particularly useful. Whenever a program tries to make an outbound Internet connection, ZoneAlarm announces it with a popup alert. You can then permit or disallow the connection, on a one-time basis or permanently. Configuring your level of protection is a simple matter of moving a few sliders. Though the free version of the software is exclusively a firewall, Check Point also offers for-pay security suites. But if all you're looking for is a firewall, stick with the free version.
Download ZoneAlarm

Comodo Firewall Pro
ZoneAlarm is extremely popular, but that doesn't automatically make it the best free firewall you can find. One formidable contender is Comodo Firewall Pro, which independent testing site Matousec rated as the top firewall. Matousec found that Comodo offered the highest level of antileak protection, one measure of a firewall's effectiveness. Comodo offers true two-way firewall protection, is highly configurable, and (unlike most other firewalls) provides a great view of your system and your Internet connection.
Download Comodo Firewall Pro

Avast
Tired of dealing with bloated, overpriced security suites that bog down your system and cost an arm and a leg, when all you want is antivirus software? Then get Avast, a superb antivirus program that's free for home and personal use. Because it's a lean piece of software, it imposes a relatively light burden on system resources and RAM. Despite this, it kills viruses in their tracks and has plenty of extras, including live scanning to prevent viruses from infecting your PC in the first place. Avast can scan regular and Web-based e-mail for viruses, too, and it protects against instant messaging viruses, peer-to-peer dangers, and more.
Download Avast

AVG Anti-Rootkit
One of the most feared types of malware is the rootkit--malicious software that many types of antimalware can't detect. Not uncommonly, bad guys use rootkits to hide Trojan horses, which can then be used to take over your PC without your knowledge. AVG Anti-Rootkit's sole purpose is to find and kill rootkits. Run it and it scans your PC, sniffing rootkits out and removing any it finds. Note that this utility doesn't work with Windows Vista.
Download AVG Anti-Rootkit

Spyware Blaster
Some of the nastiest kinds of spyware--autodialers, home page hijackers, and others--install themselves as ActiveX controls. Spyware Blaster protects you against them, blocking the installation of ActiveX-based malware and other types of spyware, and eradicating tracking cookies that might otherwise invade your privacy. The program works with Firefox, Opera, or Internet Explorer, and it prevents your browser from being diverted to dangerous sites. One particularly nice touch is the utility's System Snapshot, which (as you'd expect) takes a snapshot of your PC; if your computer gets infected later on, you can revert to the clean version.
Download Spyware Blaster

Assessing Risks to Your System
Is it safe or isn't it? Whether you're asking this question about your own system, a site you'd like to visit, or a link you're tempted to click, you need the right tools to help you understand the level of risk involved. These utilities appraise the situation and deliver an informed assessment of where you stand.

AOL Active Security Monitor
Not being a big fan of AOL in general, I was initially leery about downloading and using this free tool. But this simple, straightforward application looks at the security of your PC, reports on what it finds, and makes recommendations. It checks to see if you have antivirus software installed and, if so, whether the definitions are up to date. Then it does the same for antispyware, tests whether you have a firewall enabled, and checks for peer-to-peer software that could pose a danger. The monitor doesn't have any protective capabilities itself, but it warns you if you need some. Be aware, however, that the software doesn't work with Windows Vista. And take its recommendations with a grain of salt: It touts for-pay AOL software such as the AOL Privacy Wall over free software that may be better. Still, if you're looking for some quick security recommendations, it's worth the download.
Download AOL Active Security Monitor

McAfee SiteAdvisor
On the Web, unlike in the real world, it can be hard to recognize a bad neighborhood when you're wandering around in it. There are no boarded-up windows, no empty storefronts, no hard-looking men lounging on corners or in doorways. In fact, the prettiest and most inviting Web site may harbor all kinds of malware. That's where the McAfee SiteAdvisor comes in. It warns you when a Web site that you're about to visit--or are already visiting--may be dangerous. You install it as an Internet Explorer toolbar or as a Firefox plug-in. Then when you search with Google or some other search engine, it displays color-coded icons next to each search result, indicating whether the site in question is safe (green), questionable (yellow), or clearly unsafe (red). It checks sites for downloads that may be dangerous, and for evidence that they will send you spam if you give them your e-mail address. The toolbar offers similar reports about the sites you're currently visiting.
Download McAfee SiteAdvisor

LinkScanner Lite
This is another good tool for determining whether a Web site harbors dangerous content. Open LinkScanner Lite and type in a site URL, and the utility checks the site for dangerous scripts, bad downloads, and other hazardous content. It also warns you about phishing sites and other potentially fraudulent online operations, and it integrates with search sites in much the same way that McAfee Site Advisor does, putting icons next to search results to indicate whether they are dangerous or not. Unlike Site Advisor, though, it doesn't check whether sites harbor adware or spyware.
Download LinkScanner Lite

Internet Threat Meter
Every day, it seems, new threats hit the Internet. Symantec's Internet Threat Meter keeps you informed about the latest arrivals and includes a link to a Symantec site where you can get more information and find fixes. The program runs as a nifty little widget in Windows XP, or as a Sidebar Gadget in Windows Vista, gathering data about the latest threats and reporting the results to you.
Download Internet Threat Meter

Trend Micro HijackThis
Like it or not, no single antispyware program can detect and eradicate all spyware. Consequently your favorite antimalware utility doesn't fully protect you. If you suspect that you've been victimized by spyware, but you haven't been able to track down the source of the trouble using your usual diagnostic software, give HijackThis a try. It thoroughly analyzes your Registry and file settings, and creates a log file reporting its results. If your system is infected with spyware, that file will contain clues about the particular type you're dealing with. Though an expert can analyze the log to try to track down the problem, you shouldn't try to do any advanced analysis yourself unless you possess relevant expertise. Instead, simply upload the log file to a HijackThis Web site, and ask the community there to analyze it for you.
Download Trend Micro HijackThis

Covering Your Tracks and Cleaning Up
Encrypting private information, disabling potentially harmful scripts, and cleaning up accumulated detritus are all ways to strengthen your security. These downloads help you keep things safe and orderly.

Kruptos 2
Worried that someone may gain access to your most private files? Kruptos 2 uses powerful, 128-bit encryption to scramble files and folders so that only you can read them. It's particularly useful for USB flash drives and portable storage devices, which you can encrypt in the entirety. Kruptos 2 also lets you create self-extracting, encrypted archives; shred deleted files so that all traces of them vanish from your hard disk; and even disguise the filename when you encrypt a file.
Download Kruptos 2

Transaction Guard
This freebie from commercial security vendor Trend Micro is actually two pieces of security software in one. First, it's a spyware detector and eradicator that monitors your system in real-time for spyware and kills any it finds. Second, it introduces a "secret keyboard" to ensure that passwords and other sensitive information aren't stolen over the Internet. When you visit a site that asks for a password, instead of typing in the password, you enter it on the secret keyboard, which copies the password to the clipboard, from which it gets pasted directly into a Web form. The software runs as an ActiveX control in the System Tray.
Download Transaction Guard

CCleaner
When you surf the Web, you pick up many traces of your Internet activity. Your PC swells up with temporary Internet files, a history list, cookies, autocomplete entries, and lots more. In addition, programs create temporary files, file lists, and other bits of effluvia. Windows itself constantly monitors what you do, and records information about it in logs. In fact, a snoop could easily gather a great deal of information about you from stuff that's junking up your PC. CCleaner rids your system of all such traces. Not only does it enhance your privacy, but you'll regain hard disk space as well. When I used this utility for the first time, it deleted a whopping 835MB of files.
Download CCleaner

NoScript
Among the biggest dangers you face when surfing the Web are boobytrapped Java and JavaScript scripts and applets. Evil doers can disguise these harmful pieces of code as useful tools, or can hide them completely while they perform their nasty routines. Unfortunately, there's no practical way for you to separate the good ones from the bad ones. But NoScript, a free Firefox extension, prevents all JavaScript and Java applets from running, except on sites that you designate as safe. The extension presents you with a list of safe sites, which you can add to. NoScript tells you when it has blocked Java or JavaScript on a site. For added protection, this remarkably powerful and flexible tool also blocks Java, Flash, and other plug-ins on sites you don't trust.
Download NoScript

File Shredder 2
Delete a file and it's gone from your PC, right? Wrong. Even after you delete a file and flush it from your Recycle Bin, special software can re-create it. Of course, in general, you'd like files to stay deleted when you throw them away. File Shredder 2 overwrites any file or folder with a random string of binary data--multiple times. You have a choice of five different shredding algorithms, and using the program is a breeze: Just choose your files, tell the program to shred them, and they'll be gone forever.
Download File Shredder 2

Freelance writer Preston Gralla is author of Windows Vista in a Nutshell .