generate barcode using vb.net Protecting Yourself from Unsafe and Unwanted Software in Visual C#

Paint UPCA in Visual C# Protecting Yourself from Unsafe and Unwanted Software

ActiveX controls are small programs that run inside the browser window to enhance the functionality of a website, using a technology developed by Microsoft. They re used for such things as enabling the capability for you to play games with other internet users, displaying stock tickers, and displaying animation. Microsoft s various update sites Windows Update, Microsoft Update, and Office Update 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 essentially have full access to your computer s resources, although they are subject to some security restrictions.

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 may 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 .

A default installation of Windows Vista contains dozens of ActiveX controls, some of which are highly specialized. In the past, unsavory operators have discovered flaws in these installed controls and devised exploits that take advantage of these flaws on unpatched machines to install unwanted or hostile code. An important security improvement in Internet Explorer 7 requires that you opt in with an additional layer of approval for these ActiveX controls. The first time you encounter a webpage that attempts to use a previously installed but never-used ActiveX control, Windows prompts you to give your permission, using a message in the Information bar, as shown in Figure 27-6.

Figure 27-6 If an unfamiliar website tries to use an obscure ActieX control, Internet Explorer blocks the attempt with this display. Approe the action only if you re certain it s safe.

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. In the ActiveX Controls And Plug-ins section, adjust any of the options shown in Table 27-1 on the next page.

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Description Disable (default) means that a webinstalled but unused ActiveX control permission (enabling this option turns off the new opt-in ActiveX feature) . Disable (default) means that potentially dangerous custom objects called DHTML scriptlets won t be allowed to run in webpages . Disable (default) displays the Information bar before allowing downloads; choose Enable to skip the Information bar and display a dialog box for all ActiveX controls . Enable (default) allows scripts and programs to use an ActiveX control; choose Disable or Administrator Approved to tighten security . Disable (default) keeps ActiveX controls from using video and animations without invoking the normal media player context . Prompt (default) requires that you confirm before installing a signed control; choose Disable to prevent installation . (Note: We strongly caution against choosing Enable, which weakens security to an unacceptable level .) Disable (default) blocks installation of any unsigned control; choose Prompt if you need to install a custom control that is unsigned but trustworthy . (Note: Again, we strongly caution against choosing Enable, which weakens security to an unacceptable level .) Disable (default) blocks any attempt to use an ActiveX control that is not specifically approved for use with scripts; choose Prompt to allow this type of activity on a case-bycase basis . (Note: As noted for the previous two settings, we strongly caution against choosing Enable, which weakens security to an unacceptable level .) Enable (default) allows ActiveX controls to function, subject to other security settings; choose Prompt to approve each control as it s used, Disable to block use of all ActiveX controls, or Administrator Approved to allow only those that have been flagged as acceptable by an Administrator Administrator .

Allow previously unused site can use a previously ActiveX controls to run only with your explicit without prompt