What are ActiveX controls?
ActiveX controls
are nothing more than Windows program modules
contained in dynamic link libraries (DLL's). What
makes an ActiveX control different from a plain old DLL
is that the functions and data in an ActiveX control DLL
conform to a standardized object-oriented paradigm
invented by Microsoft. This means that certain
programs that are "ActiveX aware" can directly import
(or embed) the ActiveX control. Such programs are
commonly referred to as ActiveX containers.
ActiveX container programs are abundant, if not
ubiquitous, and include the Microsoft Office
programs such as Word and Excel and, of course, Internet
Explorer.
Stated another way, an ActiveX control is simply a
computer program that is designed to run inside of
another computer program. ActiveX controls are
just like any other Windows program. They are not
limited in any way, and can do anything that any other
Windows program can do. All they need are
container programs to run in.
ActiveX controls or applets generally have considerable
power and performance advantages over Java applets.
And, of course, unlike a Java applet, an ActiveX control
can be readily used by other ActiveX container programs,
such as Excel, Matlab, or Mathcad. However, along
with this ActiveX power, comes potentially a greater risk.
Just like in life, more power requires more
knowldege and more responsibility.
This means
that a user must exercise some caution when choosing to
run an ActiveX control on his/her system—the same
caution that is required when installing any software.
The reason for caution is that, unfortunately, not all
software works properly. In fact, bad software can
adversely affect your system performance, and can be
hard to get rid of. And, even more unfortunately,
there does exist a profusion of malevolent software that
is actually designed to damage your system or steal data
from your system. Such software, commonly referred
to as viruses, could
be contained in an ActiveX control. This is why
Internet Explorer warns the user about installing an
ActiveX control. You must trust the source of the
ActiveX control, just like you must trust the source for
any software that you put onto your computer.
Java
applets, on the other hand, provide a layer of
separation between the applet and the local file system.
The Java Virtual Machine, or JVM, is the extra layer of
software that must be installed for the Java applet to
run. Java applets cannot access the full power of
the computer system which greatly reduces the risk from
malevolent software. |
What happens when I
"install" an ActiveX control?
Here is what
happens when you choose to allow Internet Explorer to
install an ActiveX control on your system. First,
the control is copied from the internet and put into a
special directory on your computer file system.
The location of this directory depends on your version
of Internet Explorer, and probably also on your version
of Windows. ActiveX controls are really DLL's that
typically have a file extension of *.ocx. So you
can easily search your system to find where the ocx
files are located.
Once the ocx file
has been copied to your computer, it is useless and
inoperable until it gets "registered".
"Registering" the control simply means putting several
entries into your system registry to tell ActiveX
container programs about the identity, type, and
location of the ActiveX control so that they can run (or
embed) the control. This registration process
happens automatically when you "install" an ActiveX
control while browsing with Internet Explorer.
If you ever want to
disable or "uninstall" the ActiveX control then you just
do the above procedure in reverse: First you
unregister the control then you delete the file.
How do you unregister the control? One way is to
simply use the regsvr32.exe program that is provided by
your Windows OS. This program is run at the
command line by typing "regsvr32 /u FullPath.ocx".
The /u option uninstalls the ActiveX control. Of
course, first you must find the location (full path) of
the ocx file.
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