Do Virus Scanners Slow Down Your System?

Response Time Benchmarks

It is our intention to benchmark the boot time with these different security solutions installed, and we spent a lot of time testing this using GreenVantage’s WinBootInfo utility. Unfortunately, the results we recorded show a huge variance from 30 to 60 seconds, even when taken one after the other, and we’re not comfortable releasing these results even after averaging multiple iterations. What we will say is that all of the averages we recorded are between 32 and 46 seconds. With boot times ranging from 30 to 60 seconds, there probably isn’t any significant conclusion to draw.

The response time benchmarks we demonstrate below are much more consistent. We open a document in Word and a LAN-hosted Web page in Firefox. Here’s how long it takes, on average, to open these files the first time after a fresh boot into Windows:

While we do experience significant variance between minimum and maximum load times for each security software package, with six iterations averaged, we see some clear trends across Firefox and Word. Most notably, AVG, McAfee, and Trend Micro products seem to take a little longer to open files than their competitors. McAfee Internet Security, specifically, has a longer wait time to launch the test Web page.

Speaking of McAfee, with this product installed, we notice a colossal lag to launch the timer application we developed to record benchmark results. When I say colossal, I mean it takes the better part of 10 seconds to launch the tiny program—an application that executes instantly with any other anti-virus program we tested. The reason for this appears to be that McAfee’s real-time scanning method is based on checking against known application signatures. Since McAfee obviously can’t have signatures for custom-made applications, it will thoroughly scan the application in question before launch. It does seem to take longer than it should to accomplish this task. We’re asking McAfee about this and hope to have an answer before publication—otherwise, we will follow up in a future article.

Back to the results, though. The bar graphs do make it appear that there is a large variance on first load, but we’re talking about a two to five-and-a-half second spread to open Firefox and a three-to-six-second spread to open a Word document. It sounds worse than it feels, as those extra few seconds don’t seem all that obvious. Admittedly, that’s a subjective argument.

What is objective is that the same application loads much faster the second time it is launched during a Windows session:

The difference in application launch speeds is reduced to less than a second between competing security software solutions on subsequent runs of the same program. This is a short enough time span that it's difficult to notice any change at all during real-world use.

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    Top Comments
  • I think Microsoft Security Essentials should be included if possible and there is a situation that I think it is greatly affected by anti-virus software: Windows start-up.
    38
  • Avast please?
    33
  • before i read the article, my guess is Norton is the slowest and most useless....
    24
  • Other Comments
  • Great article, thanks!
    5
  • before i read the article, my guess is Norton is the slowest and most useless....
    24
  • How can u forget Avira , it's so popular & so good .
    24
  • I guess the new ones are lighter than the earlier ones for some of them....
    -3
  • well from my point of view - antivirus scanner do application loading to take a much longer time and this was proven by your tests.

    I think that AV software has no place into todays operating systems except for inexperincied users. I'm investing money to fast SSD disc to improve performace, why the hell intstall AV software to push performance back?
    -21
  • This is the kind of article that keeps me coming back to Tom's! Kudos!
    4
  • Avast please?
    33
  • talk about heavy modifications on the new set of AVs compared to the older ones ... my surprise is norton which i was expecting to cripple the system to a halt .... very nice article btw
    4
  • The test rig's CPU looks funny to me.

    Athlon II X4 645
    3.5 GHz, Quad-Core, 6 MB L3 Cache

    Isn't that a Phenom?
    -12
  • @Fip - Because when dirty viruses do their job, you'll get a headache.
    2
  • iam2thecrowebefore i read the article, my guess is Norton is the slowest and most useless....

    well i am really surprised
    13
  • @tony singh
    yes - for inexperienced user. I have no problem with viruses over 8 years. OS Patches, working under different than admin account, not using IE, and not executing every garbage downloaded from internet. And finally virtustotal page for testing for viruses if you realy need it.
    -11
  • iam2thecrowewell i am really surprised

    I get Norton Security Suite free with Comcast. I was kind of bummed when I found out that's all they have available, but so far its been good to me. I haven't noticed any adverse effects, maybe startup is s little slower.
    2
  • this is tested on a fresh install - the average system has a ~2 year old install and fragmentation and lower end hdd's, combind with a crapload of other software trying to startup - no really a real world benchmark.
    24
  • it would have been useful to see a difference in the benchmarks using different HDDs like the 5400 RPM laptop ones, 7200 RPM and SSDs, that would have made a difference
    9
  • Fip is right, cmon, it's not so easy to get a virus installed in your computer. Only real concern is about pendrive virus, otherwise, it's real hard get a virus actually, so just deactivate autorun and you're done.

    If you still think a Anti-virus is useful, look to the logs of your anti-virus, how much viruses have you executed? How much of these you wouldn't figured out even without any anti-virus? A computer virus it's not something invisible who will eat your computer's guts, it's just a program, and need to you to execute him at least one time.

    We aren't in 1996 with blaster or melissa. Tom's is supposed to be a site for tech guys, cmon, you aren't supposed to be a facebook brainless guy who don't know the difference betweek "naked gurls.exe" and "naked gurls.jpg".
    -13
  • Well the biggest slowdown you will experience with antivirus software is when you open a folder full of exe files and explorer tries to show all the icons of the executables. There is a very noticeable slowdown in that case.
    Also i would have liked a startup benchmark, because the antivirus also slowdowns somewhat the startup process.
    4
  • I think Microsoft Security Essentials should be included if possible and there is a situation that I think it is greatly affected by anti-virus software: Windows start-up.
    38
  • iam2thecrowewell i am really surprised

    Norton has VASTLY improved compared to what it used to be. I use Norton 360, and I have to say that it has been a great product.
    5
  • 2 ddragoonss
    thanks,
    AV is far from 100% protection, and could bring new problems (recently ESET NOD Smart Security causes problem with internet connection due to connection inspection / filtering ... ) For IT Pro is risk to get a virus very low, and if get one - few hours to get it out is worh instead of years of boring my pc with AV software
    -7