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DADDY BOB'S COMPUTER Q & A
June 21, 2009
Q.
When I try to read a particular web email,
Internet Explorer shuts down and I receive a
message about something called DEP with
instructions I cannot follow to turn it off.
What s DEP and how do I turn it off?
A.
DEP stands for Data Execution Prevention. It
is a security feature included in XP SP-2
and later operating systems. It is intended
to prevent a program or service from
executing code from section of memory where
it shouldn't. This is supposed to prevent
problems that can occur from something
called "Buffer Overflow".
Microsoft
explains it like this; "Data Execution
Prevention (DEP) is a security feature that
can help prevent damage to your computer
from viruses and other security threats.
Harmful programs can try to attack Windows
by attempting to run (also known as execute)
code from system memory locations reserved
for Windows and other authorized programs.
These types of attacks can harm your
programs and files.
DEP can
help protect your computer by monitoring
your programs to make sure that they use
system memory safely. If DEP notices a
program on your computer using memory
incorrectly, it closes the program and
notifies you."
There are
two types of DEP, hardware and software
enforced. CPUs that support it can mark
memory pages as non-executable. (A memory
page is a fixed-length block of main memory,
that is contiguous in both physical memory
addressing and virtual memory addressing.) In computers
with DEP supported CPUs and those that do not support DEP, software
DEP can be used.
Software
DEP works a little differently in that it
does not mark pages of memory as
non-executable, but instead prevents
overwriting files in memory. The results of
either type help to prevent code from
executing in an area of memory where it
shouldn't.
In some
rare cases, Data Execution Prevention can
have the unintended consequence of
preventing legitimate software from
executing. In these cases, the affected
software can be flagged as being allowed to
execute code in those parts of memory. This
may be the case with this subject email
problem.
If the
email in question that is causing the
problem cannot be deleted then it may be
prudent to temporarily turn off DEP to allow
it to be opened and then read and deleted.
Here's how to turn off DEP for a given
program or service. The process is very
similar for Windows XP and Vista.
Right
click on My Computer and select properties.
(Note that in XP it is "My Computer" while
in Vista it is just "Computer".) In XP,
click the Advanced tab. In Vista, click on
Advanced System Settings. When the dialog
opens, click on the Settings button in the
Performance section.
Click on
the Data Execution Prevention tab. By
default, DEP will be turned on for essential
Windows programs and services only. This is
the preferred setting. You can choose to
turn it off for any program by choosing to
Turn on DEP for all programs and services
except the ones you list here. After
selecting this choice, click the Add button
and then locate the program you want to
exclude from DEP. In this particular case,
it would be C:\Program Files\Internet
Explorer\iexplorer.exe.
When you
get the warning about turning off the DEP,
click OK, then OK again to close the dialog.
Now, go try to read the problem email and
correct whatever it is that is causing the
problem. Deleting the email is probably the
most prudent action. Now, go back and remove
the exception you just created, and reselect
to Turn on DEP for essential programs and
services.
Note that
near the bottom of the dialog is a message
about your CPUs ability to support hardware
based DEP. In some cases like with the Intel
Adam CPU there will not be any message
displayed. If this is the case, hardware DEP
is not supported. |
