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How much does antivirus software slow one's computer down?

Posted on 2006-11-09
Medium Priority
Last Modified: 2007-12-19
I was thinking about purchasing Norton AntiVirus 2007, but was wondering whether it is significantly faster than Norton AntiVirus 2006?  

In general, will Norton or some other competitor's antivirus software slow my computer down more?  

Lastly, on a dual-core machine, should I worry about this much less (the slowing down), or is this more of a disk-access issue?

Thanks for the response in advance.
Question by:wdwcuwa
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Expert Comment

ID: 17911792
On a dual core machine I wouldn't really be too worried about CPU usage on your computer.  Anti-Virus applications are more disk intensive then anything else.  Although at times they can be more memory intensive then most applications, it really should not be much of an issue if you have over 256 Mb of Ram.

The real issue like stated above is these applications can be more Disk Intensive.  To get around this, it is best to schedule times to scan the computer, such as periods of inactivity.

While regularly scanning downloaded files etc.  You should not notice much of a slow down.  I really don't know the differences between the 2006 and 2007 versions of NAV, so I really couldn't help you there.

LVL 17

Expert Comment

by:Dushan De Silva
ID: 17911863
In my dualcore machine having norton 2000 version. I brought this PC two months ago with SATA hard drives, 512MB Ram..etc. But till this moment no problem for me. But when I'm starting the scanning of the PC from it one processor is getting busy around 50%. But with other processor I can do other works. But its it slower than normal working environment. But other than scaninig time I don't having any problems. I'm not plannig to update my anti virus guards to 2006/7 yet since my PC providers installed it and I can take latest virus difinitions and its not slow like norton 2006. I have used norton 2006 earlier(not in a dualcore) Its very slow. Upto this moment I dont have any problem in my machine with norton 2000.

BR Dushan
LVL 23

Expert Comment

by:Mohamed Osama
ID: 17912582
Norton versons  after 2005 are the most CPU /RAM  hungry antivirus I have seen , since you say its a dual core machine , I dont think this will be much of an issue , but as darkstar245 mentioned the autoprotect feature can be VERY Disk Intensive, you can change the default settings for autoprotect , background scans to improve that .

one last piece of advice , compare other AV products to symantec before the purchase , I know for a fact some AV programs are way better when it comes to detection and much more resource friendly ( NOD32 , Kaspersky,etc..)
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Expert Comment

ID: 17918257
To give you an insight

I have been a long term user of Norton antivirus since its early versions up to 2004, afterwitch I switched to Nod32 due to its CPU/ Ram hungry nature from 2005 and upwards like Amdin3k implied. In addition to its resource consuming tendency it failed to detect couple of threats that Nod32 detected, for example the notorious MS Blast, that Nod32 intercepted while NAV200x on couldn't in the begining.

Been a year since I switched to NOD32, not only it offered better virus detection, but hardly took any system resources. Didn't slow down the system even while updating its definition files on daily basis.

Straightforward to use, simple yet a powerful program.

There is a 30 days fully funtional trial version if you are curious. 10mb at most, I suggest you give it a shot for a while and see the difference I discussed above for yourself :)


Expert Comment

ID: 17923712
Hi wdwcuwa,

Steer clear of Norton for all reasons stated above.

Most anti-virus programs use techniques to prevent rescanning of a file if it hasn't changed.  In the case of one anti-virus product (it hasn't been mentioned here yet), critical areas of a file were scanned very quickly to create checksums to determine if it was a 'new/changed' file, then scanned properly if it is.  The same company now hooks into Windows 2000 (and above) operating system calls, where the OS itself assigns a code for each file it opens.  If that file is changed, then it is given a new code the next time it opens.  For each new code, the AV program will scan the file.  If the OS doesn't assign a new code, the AV program doesn't touch the file.  All codes are reset at reboot.

The net effect is that checksumming is very quick anyway, and the newer method is even quicker, except that startup takes a fraction longer.

I hope this helps,
Steve : )
LVL 38

Accepted Solution

Rich Rumble earned 500 total points
ID: 17927763
Your going to get a lot of peoples experiences/opinions, and heres mine... McAfee allows you to set the CPU priority to use during a scan. I'm not sure if Norton is this way, i think it is, when you access a file on the HD, the AV scans it, if it's cool, you run that exe, if it's infected your prompted. There is also another scan taking place on the PC (at least with McAfee, it's looking at all the files on the HD, with a very low priority), and when you access a file or directory, it needs to scan that dir and or file too, adding the the CPU load. What really slows a PC down, no matter who makes it, is a full scan, the faster you want it to scan the more CPU it's going to use. Most AV's aren't multi-threaded, so 1 CPU will be pegged and the other will do the other task's. In a dual-CPU setup you'll feel the "crunch" a lot less than on a single. Intel's hyper-threading you may feel a bit more of a lag than with two separate physical CPU's, or even a dual-core system. McAfee again allows you to throttle the full scan, it will go slower, but you will only use a certain amount of CPU.

Use best practices and you don't need anti-virus or anti-spyware 99.9% of the time. That .1 percent still exists... and even then you've got the 0-day issue to likely get past. In Vista, M$ thinks very highly of best practices, as Mac's, and *nix OS's like Linus have for generations...
-rich (my wife is non-admin on her machine, no spyware or viri for 4 years, XP pro running McAfee)

Author Comment

ID: 17984827
Thank you all for the helpful and insightful responses.  I have definitely begun to look into NOD32, Kasperksy, and additionally BitDefender.  However, I have one follow up question: Are these programs disk intensive only when they are running/scanning, or are they also disk intensive when they are in "auto-protect" mode?  Moreover, what exactly is "auto-protect" mode?

The real concern is that I have dictation software that deals with very large data files containing a language model, and I am wondering if Norton will get in the way every time I try to read that file.  Later on, when my computer gets bogged down from all the programs I've installed, will auto-protect slow me down?

Thanks again.
LVL 38

Expert Comment

by:Rich Rumble
ID: 17984848
I can only speak to McAfee, it's On-Access scan scan's files as you open them, and add's no real lag with it on or off, I can't tell the difference. Full system scans are where the resources get hogged more I think for all AV. With Best Practices there is no added overhead :)

Expert Comment

ID: 17985849
These programs are disk intensive doing a full disk scan than when they are in auto-protect mode, but it still depends on how you configure it.  For example, in auto-protect mode (which basically checks if a file is clean before it's opened), only certain parts of the file are scanned.  Even this can be configure to scan the entire file in most cases - bad move!!  Anyway, with modern computers you really need not worry about any significant impact on your ability to use your computer.

If we're talking large files (multi Gb) that change often, yes - they may have some affect on your computer's speed whilst reading these files, but if it's that bad you can normally set exclusions for that filetype.

Different people think different AV programs are good/bad based on their personal experience.  Why not take up some trial versions of the anti-virus software that appeals to you and see?

Steve : )
LVL 17

Expert Comment

by:Dushan De Silva
ID: 18008875
Norton 2000 AV version is not much taking resources other than scaning time.(from my experience). But Norton 2005 is always eating the resources.

BR Dushan

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