Using Internet Explorer 8 : Security and Privacy Options (part 2) - Protecting Yourself from Unsafe and Unwanted Software

3. Protecting Yourself from Unsafe and Unwanted Software

With the addition of Windows Firewall, Internet Explorer's Protected Mode, and Windows Defender, it has become much easier to keep unwanted software off of your computer and to remove it when it does get installed. The use of an antivirus program and sound surfing habits help increase safety and security to a very high level. This section examines some best practices that help to keep your computer free from unwanted software.

3.1. To Trust or Not to Trust?

Microsoft offers a digital signing technology, called Authenticode, that can be used to guarantee that an executable item comes from the publisher it says it comes from and that it has not been changed, deliberately or otherwise, since it left the publisher's hands. The digital signature verifies each bit of the signed file by comparing it to a hash value; if even a single bit of the file has changed, the comparison fails and the signature is invalid. Windows 7 blocks installation of any code that has an invalid signature—by definition, this indicates that the program file is corrupt (possibly because it was damaged during downloading) or that it has been tampered with.

A digital signature doesn't promise that the signed item is healthy and benevolent. It confirms only that the bits you're about to download are the authentic work of a particular party and haven't been tampered with on their way to you. However, it is prudent to regard an unsigned item, or an item without a valid signature, as a potential threat.

Assuming the signature is valid, you can use the information contained within that signature to make an additional determination—do you trust the person or organization that attached the signature to the file? If the publisher is reputable and the Security Warning message reports that the item has been digitally signed, you must then decide how much confidence you have in the publisher.

Normally, you make choices about whether or not to install a signed item on an individual basis. But you can choose to trust a particular publisher and allow its software to be installed automatically without any prompting. Or you can decide that the publisher of a particular program is not trustworthy and you do not want any products from that publisher to be installed on your computer, under any circumstances.

3.2. Blocking Potentially Unsafe Downloads

How does deceptive software end up on a computer? The simplest route is the most direct: you click a link on a webpage or in an e-mail message that leads directly to an executable file. For example, an advertisement might make extravagant or alarming claims about a free program, perhaps even embedding the link in a pop-up window that looks like a warning dialog box generated by Windows. When an unsophisticated computer user clicks the ad, the program offers to install as an ActiveX control via an Authenticode dialog box, which can easily be mistaken for an official Windows stamp of approval.

In some cases, the setup routine for one program surreptitiously installs additional programs in the background. When we installed one widely used song-swapping program in a previous version of Windows, for instance, we found that it installed four well-hidden add-ons along with the main application, resulting in an increase in pop-up advertisements and changes to the way the browser handled search requests and mistyped URLs. The most vicious types of deceptive software typically attempt to exploit security holes to install themselves automatically, without your approval or even your knowledge.

It should come as no surprise that the makers of this sort of software employ all sorts of tricks to mislead, deceive, and cajole you into installing their wares, by extolling the program's benefits and glossing over or omitting any mention of its undesirable behavior. For someone with a basic understanding of computer security issues, the principal security concern when browsing is to ensure (insofar as it is possible) that anything you download is safe and that any potentially undesirable behavior is fully disclosed. If you share a computer or network with unsophisticated computer users who cannot reasonably be expected to consistently reject unsafe software, your goal should be to prevent them from having to make potentially confusing choices in the first place.

When you click a link that points directly to an executable program file, Windows displays a Security Warning dialog box like this:

If you click Run, Windows downloads the file to a temporary location and, when the download is complete, immediately runs the executable program as if you had double-clicked it yourself. If you click Save, you can download the file to a folder on your hard disk. After the file is downloaded, you can click the Run button in the Download Complete dialog box or click Open Folder to open Windows Explorer, display the contents of the folder in which you saved the file, and double-click the file.

What happens next depends on the file type and whether the file is digitally signed:

• If the downloaded file is not executable, you see a warning dialog box asking whether you want to allow the program associated with that file type to open the downloaded file. In the example shown here, Windows is attempting to open a Microsoft Office Word document using the Microsoft Word Viewer program:

  
  

  

  
  

  You can allow or refuse the request. If you click Allow and select the Do Not Show Me The Warning For This Program Again option, your choice is saved and applied to all further examples of this type of content. If you click Don't Allow, Windows ignores the Do Not Show Me The Warning For This Program Again option even if you select it.

• If the download is an unsigned executable file, you see a second Security Warning dialog box when you attempt to run it.

• If the download is a signed executable file, you see a UAC dialog box that requires you to enter an administrator's credentials to continue.

If you're certain that the program is safe, you can continue with the installation.

3.3. Controlling ActiveX

ActiveX controls are small programs that run inside the browser window to enhance the functionality of a website. They're used for such things as enabling you to play games with other internet users, displaying stock tickers, and displaying animation. Microsoft's various update sites use ActiveX controls to compare installed patches and updates on your system with those available on Microsoft's servers. ActiveX controls contain binary code and, like executables that you run from the Start menu or a command line, they have full access to your computer's resources, although they are subject to some security restrictions.

Note:

You cannot download an ActiveX control, scan it for viruses, and install it separately. ActiveX controls must be installed on the fly. Although the inability to scan for viruses in advance might sound like a security risk, you're protected from known viruses if you've configured your antivirus software to perform real-time scanning for hostile code. If the ActiveX control contains the signature of a known virus or worm or engages in suspicious behavior, the antivirus software will intercept it and refuse to allow the installation to proceed. As with any program you download and install, of course, you need to exercise caution and ensure that the download is safe before allowing it on your computer.

Some businesses refuse to allow the use of any ActiveX control that is not approved by an administrator. Others disallow all ActiveX controls. If you need to tighten the security settings imposed on ActiveX controls in the Internet zone, choose Internet Options from the Tools menu in Internet Explorer. On the Security tab, click Internet, and then click Custom Level. Then adjust options under the heading ActiveX Controls And Plug-Ins.