Security Secrets the Bad Guys Don't Want You to Know Rogue scripts, fake antivirus programs and infected PDFs: Defend yourself against the web's most insidious threats.

You know to keep your antivirus program and patches up to date, to be careful where you go on the internet, and to exercise online street-smarts to resist being tricked into visiting a phishing site or downloading a Trojan horse.

But when you've got the basics covered, but you still don't feel secure, what can you do? Here are a few advanced security tips to help you thwart some of today's most common attacks.

Remember, however, that security is all about trade-offs. With most of these tips, what you gain in security, you lose in convenience. But hey, it's your computer. Be as paranoid as you want to be.

Avoid Scripting
This may be the one piece of advice that will do most to keep you the safe on the web: Steer clear of JavaScript, especially on sites you don't trust.

JavaScript is very popular, and for good reason. It works in almost all browsers, and it makes the web a lot more dynamic. But it also enables bad guys to trick your browser more easily into doing something that it shouldn't. The deception could be something as simple as telling the browser to load an element from another web page. Or it could involve something more complicated, like a cross-site scripting attack, which gives the attacker a way to impersonate the victim on a legitimate web page.

JavaScipt attacks are everywhere. If you use Facebook, you may have seen one of the latest. Lately, scammers have set up illegitimate Facebook pages offering things like a free $500 gift card if you cut and paste some code into your browser's address bar.

That code is JavaScript--and you should never add it to your browser. "Scammers use this technique to open up unwanted surveys, fill your social networking profiles with spam or even to send you to phishing pages," says Chris Boyd, a security researcher with Sunbelt Software.

But miscreants can add JavaScript to hacked or malicious web pages, too. To avoid attacks there, you can use a free Firefox plugin called NoScript that lets you control which websites can and cannot run JavaScript in the browser. NoScript goes a long way toward preventing rogue antivirus programs or online attacks from popping up when you visit a new website.

By blocking scripting everywhere and then using NoScript to build a whitelist of trusted sites, you can derail most of the so-called web drive-by attacks that currently plague the internet.

NoScript also comes with a cross-site scripting blocker. Cross-site scripting has been around for a while, but these days bad guys are using it more frequently than ever to seize control of online accounts on sites such as Facebook and YouTube.

If you don't use Firefox, you still have some options for cracking down on scripting. Like Foxfire users, Google Chrome users can disable JavaScript universally and then build a whitelist of sites where it's permitted.

Unfortunately, neither Internet Explorer nor Safari has a NoScript equivalent, but IE users can adjust their Internet Zones security settings to require prompts before scripting. And IE 8 includes new cross-site scripting protection to ward off some attacks.

Disabling JavaScript in Adobe Reader can help, too. According to Symantec, last year nearly half of all web-based attacks were associated with malicious PDF files. If victims had adjusted their settings to make it impossible for PDFs to execute JavaScript, they would have thwarted most of those attacks.

To disable JavaScript in Reader, click Edit, Preferences, JavaScript and then uncheck the Enable Acrobat JavaScript box to the right of the window.

The downside of all these defensive tactics is inconvenience. With scripting disabled in your browser, many animations, movies, and dynamic web pages simply won't work--and many users get frustrated by the never-ending cycle of opening a web page, seeing that it doesn't work properly, and then choosing to allow scripting on that page.

The same holds true for Reader, where PDF-based forms may not submit properly if you've disabled JavaScript; nevertheless, many people don't mind simply turning on Reader's JavaScript whenever they need it.

Back Out of Rogue Antivirus Offers
Far too many people have had this experience recently: You're surfing the web on a totally legitimate site when a scary-looking warning message pops up suddenly. It tells you that your computer is infected. You try to get rid of it, but more windows keep popping up, urging you to scan your computer.

If you do this, the scan invariably finds security problems and offers to sell you software that will take care of the problem. This is rogue antivirus software. The only thing the software does is put money into the pockets of criminals.

Rogue antivirus programs have emerged as one of the most annoying security problems of the past few years. To the victim, the pop-ups can seem like an infection themselves. Every time you try to close a warning window, another one appears.

Here's what you do: First off, never buy the software. It simply doesn't work, and often it will trash your system. Either press Alt-F4 to close your browser directly or press Ctrl-Alt-Delete to open your system's task manager and shut the browser down from there. Closing the browser generally puts an end to the pop-up problem.

Another way to steer clear of rogue antivirus attacks is to be careful when reading up on a hot news story. The bad guys follow Google Trends and Twitter's Trending topics, and they can quickly promote one of their malicious web pages to the top of Google search results.

Google tries to control this activity, but when a breaking news story is involved, the evil doers are often one step ahead. "Cut down on the risk of being affected by only reading news sources you trust, or--at the very least--search Google News for news services you haven't seen before," says Sunbelt's Boyd.

Don't Depend on Microsoft Word or Adobe Reader
They're extremely popular programs, but Microsoft Office and Adobe Reader are not the strongest applications from a security perspective--especially when it comes to opening files that you think are probably okay but aren't sure about.

Most bad guys subscribe to a big-tent theory of troublemaking. When they plan an attack, they usually aim at the most widely used software programs, which is one reason why Windows gets hit so much more often than Linux or Mac operating systems.

One way to stay a step ahead of them is to use less-popular apps that crooks target relatively infrequently. Many security experts open their PDF files in alternative readers such as Foxit Reader or PDF Studio. Similarly, you can check .doc and .ppt files in OpenOffice. The downside is that, in a nonstandard application, files may not look exactly as they should. This drawback might make such apps unsuitable for daily use, depending on your needs, but even so you should consider using them to open dubious documents in.

Use a Service Like Gmail or VirusTotal to Check Documents That You Do Open
Why do security experts use alternative PDF and .doc readers?

They've warned us for years not to open attachments that come from untrusted sources. Strange .exe files are a sure sign of trouble, but hackers have also found ways to break into computers by tricking users into opening maliciously encoded documents. The vast majority of these attacks take advantage of known flaws in older programs; but in addition, new attacks--called zero-day attacks--periodically pop up, exploiting flaws that software makers haven't yet patched.

By now you know to find an alternative document reader, but if that doesn't work for you, consider adopting other methods to double-check documents and avoid viruses.

One approach is to let Google do the checking for you. Forward attachments to a Gmail address, and Google's filters will scan it for malware. Then, you can convert the document and read in Google Docs to see whether it's legit.

Another tip is to submit files to Virustotal. This free scanning service runs your file through 41 antivirus scanning engines. If any of the programs identifies it as malicious, Virustotal will let you know

Know What Programs You Use, and Verify That They're Up to Date
Haven't used an application in years? Go to your Windows Control panel and uninstall it! (The Windows 7 version of the Control Panel is shown here.) The old version of RealPlayer you downloaded a few years ago may be nothing more than a security hole today. If you don't use a program, consider uninstalling from your PC.

To trim unwanted apps, visit the Windows Install/Uninstall section of the Control Panel. As a rule of thumb, if you're not using a program, lose it.

From a security perspective, every program--especially a widely used app--is just another path that hackers can use to break into your system. A useful security tool is the Secunia Online Software Inspector, which scans your PC for out-of-date software.

Use Plugin Check, a handy Mozilla feature, to see whether your browser's plug-ins need updating.But don't stop there. On this helpful Mozilla page, you can check to see whether your various browser plug-ins--for Chrome, Firefox, IE, and Opera--need updates.

It's also a good idea to check your Facebook applications to make sure that you don't have the Facebook equivalent of software bloat. While logged in, click Account, Application Settings, and see what apps you have installed. If you don't use one, delete it.

Sharpen Your Password Game
People have to remember too many passwords on the internet. Everyone knows this, but most of us get around the problem by using the same username and password over and over.

Hackers know this as well, and they're happy to use it against you. Often they steal a person's password and user name, perhaps via a phishing attack, and then try that combination on other popular services--Facebook, Gmail, PayPal, Yahoo--to see if it works there, too.

Luckily free and simple password management tools, such as KeePass Password Safe, are available to keep track of your passwords for you. They are a bit more work--you may tire of constantly jumping between a password manager and your browser every time you want to log into a website, but remember that security always involves trade-offs.

If you use the Firefox browser, you can try the KeeFox plug-in, which integrates KeePass's password management with your browser. (Products like these "keep people on the good practice of having secure and separate passwords for everything, but keeps them from having to memorize them," says Wesley McGrew, a security researcher with McGrew Security.

Robert McMillan covers security issues for the IDG News Service.