Mac Virus/Malware FAQ

Discussion in 'Mac Basics and Help' started by stridemat, Jul 23, 2014.

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  1. stridemat, Jul 23, 2014
    Last edited by stridemat: Jul 23, 2014

    stridemat Moderator


    Staff Member

    Apr 2, 2008
    Credit should go to GGJstudios for the original text.

    You DON'T have a virus on your Mac!
    If you want to know why this is true, read on.

    The term "virus" is commonly but erroneously used to refer to all types of malware, adware, and spyware programs that do not have the reproductive ability of a true virus.

    The bottom line is this: as a Mac user, your chances of being affected by a virus, trojan or other malware are extremely slim, unless you've been careless about where you get software and when you enter your administrator password.

    If you're experiencing a problem or unexpected behavior with your Mac, there's better than a 99.9% chance that it's something other than a virus or other malware.

    From Symantec:

    What is scareware?
    Another type of hoax is referred to as scareware. It's a bogus virus warning that pops up when visiting some websites, and looks something like this or this (on iPads). If you take a close look, you'll see the popup refers to a Windows system, which obviously doesn't relate to Mac OS X. It can't harm your Mac at all. Just close the site, clear your browser's cache and cookies, and you'll be fine. Sometimes these scareware sites will generate a never-ending loop of popups, to the point that you must Force Quit your browser. Such scareware sites are usually intended to lure a Windows user into clicking the links to install bogus "antivirus" software, which is typically a trojan. Even if you click the links on a Mac system, it can't install anything, because Windows executable files can't run on Mac OS X.​

    There are NO viruses in the wild that affect Mac OS X at this time.
    If this changes, I will update this post. According to noted computer virus expert Paul Ducklin, in order for a virus to be considered in the wild, "it must be spreading as a result of normal day-to-day operations on and between the computers of unsuspecting users." This definition excludes "proof of concept" code that is used in a testing situation under strictly controlled conditions, and which poses zero threat to average computer users.

    In the past, there have been a few viruses that ran on older versions of the Mac operating system (Mac OS 9 and earlier), but they do not run on any version of Mac OS X. Like every other OS, Mac OS X is not immune to malware threats, this situation could change at any time, but if a new virus is discovered, the news media, forums, blogs, etc. will be instantly buzzing with the news. See update below.*

    There are trojans that can affect Mac OS X,
    but these must be downloaded and installed by the user, which usually involves entering the user's administrator password. Also, Mac OS X will give you a warning when you first launch an app you downloaded from the web. Trojans can easily be avoided by the user exercising common sense and caution when installing applications. A common source of trojans is pirated software, typically downloaded from bit torrent sites.​


    Having virus protection software on your Mac is pointless, as far as protecting your Mac from true viruses, since current antivirus software cannot detect a Mac virus that doesn't yet exist, because they simply don't know what to look for. It is possible to have a virus-infected file reside on your hard drive, but since a Windows virus (like any Windows program) can't run in native Mac OS X, it would be harmless to your Mac and could not spread.

    If your situation requires you to run a 3rd-party antivirus app:
    • ClamXav is one of the best choices, since it isn't a resource hog, detects both Mac and Windows malware and doesn't run with elevated privileges. You can run scans when you choose, rather than leaving it running all the time, slowing your system. ClamXav has a Sentry feature which, if enabled, will use significant system resources to constantly scan. Disable the Sentry feature. You don't need it. Also, when you first install ClamXav, as with many antivirus apps, it may perform an initial full system scan, which will consume resources. Once the initial scan is complete, periodic on-demand scans will have much lower demands on resources.
    • Sophos should be avoided, as it could actually increase your Mac's vulnerability, as described here and here... and here.
    • iAntiVirus has a bogus malware definitions list, making their detection accuracy untrustworthy. They also make inaccurate claims about the existence of Mac malware, in order to hype the need for their product. This post will give details.


    • DON'T install pirated software, or software from untrusted or unknown sites.
    • You can't infect your Mac simply by visiting a website, opening an email attachment, or connecting to a network. You should, however, exercise reasonable caution when doing these things.
    • Be careful about giving others access to your computer, as they could download and install malware.
    • For Safari users: go to Safari > Preferences > Security > Enable Java (leave this unchecked, unless you're visiting a trusted site that requires it)
    • Make sure you install software updates when they're released, including OS X and apps
    • Only install updates from an installed app, the Mac App Store or directly from a software developer's site. Never install an update to software when prompted to do so by an advertisement on a website or an email.
    • Use ad-blockers to minimize exposure to malicious sites
    • Use trusted DNS servers
    • Go to System Preferences > Security > Firewall and make sure your built-in firewall is enabled
    • Read Mac Security Suggestions compiled by munkery

    Some users choose to run antivirus such as ClamXav on their Mac to scan for Windows viruses (it also scans for Mac threats), so the Mac user can't pass a virus-infected file to a Windows user. However, a more prudent approach is for every Windows user to be protected by their own AV software, to guard against viruses from any source, not just those that might come from a Mac user.

    Running anti-virus on your Mac to protect Windows users from malware is like covering your mouth when you cough in front of the kids, then sending them out without flu shots to a school where a flu epidemic is spreading like wildfire. Great! They might not catch anything from you, but you've left them vulnerable to the greater risk. It's wiser to make sure they have flu shots, so they're protected from infection, whether it be from you or from other people.

    If you really want to help your Windows friends, encourage them to get their own anti-virus protection installed, or offer to install it for them.​

    Some users experience a problem with being directed automatically to sites that they didn't intend to visit. This may also occur when searching with Google. You don't have a virus! It's a problem with your DNS settings, either in your Mac or in your router. Try resetting your router. Here's how to fix the problem in Mac OS X:


    As has already been stated, any appearance of significant new security threats to Mac OS X will make news headlines:

    MacDefender or MacSecurity or MacProtector or MacGuard installation package
    Apple has issued a knowledge base article on this issue, found here:

    How to avoid or remove Mac Defender malware
    Further information on MacDefender:

    trojan.osx.boonana.a Trojan
    On Oct. 26, 2010, Mac security site SecureMac posted this security bulletin:
    As with all trojans, this requires the user to unwittingly invite the infection by deliberate action (in this case, clicking on a fake video link). You cannot be infected by this trojan if you don't click on the appropriate link. You can eliminate this threat by disabling Java in your web browser.
  2. brdeveloper macrumors 68020


    Apr 21, 2010
    Well, actually being virus-free is pretty easy even on Windows these days. When someone says "Macs don't get virus!" it looks more like an advertising than a preventive approach. Even Windows is almost virus free these days. The problem is software not capable of reproducing itself like adwares, spywares, trojans, rootkits, etc.

    I'm a little bit afraid for never having got a malware on my Macs. Actually I don't know if something is being tracked by some hidden application/service.
  3. GGJstudios macrumors Westmere


    May 16, 2008
    All OS X malware that has ever existed in the wild can be easily avoided by practicing safe computing. It is really quite rare to even encounter OS X malware, unless you're being reckless with where you get software that you install.
  4. squonk2 macrumors newbie

    Dec 5, 2014
    A Trojan...?

    Thank you for all your valuable information, GGJstudios. I'm a new member and have been reading all your posts on the forums regarding viruses and malware.

    While I always use the safe computing practices you've described, my wife (not technically savvy) does not. I'm fearful she might have invited a Trojan without knowing.

    She was attempting to send an Evite online (a site she uses frequently) when a shaded gray popup window asked her to enter the word/phrase displayed in that window into an open space below. This has never happened to her on this site before. Unknowingly, she entered the phrase and her entire iMac screen started flashing black & white. She immediately quit her browser. She relayed this story to me, so I did not see it but it all sounds concerning.

    I am willing to run any recommended antivirus/malware software if warranted. Her iMac has been shut off since and I'm looking to the knowledge of others as to how I should proceed.

    Thank you for any help/suggestions!
  5. GGJstudios macrumors Westmere


    May 16, 2008
    This is a security method that many sites use to make sure their site is being accessed by a real person, and not a bot (automated software). It's called a CAPTCHA test, and it's completely harmless.

    It sounds like the site may have had a problem properly displaying the page. It doesn't sound like anything related to any known malware. Clear your browser's cache and cookies and try it again. Chances are very good that it's just a glitch on the site, and nothing to be concerned about.

    If you need to run a scan for your peace of mind, you can install ClamXav and run a scan. I doubt it will find anything, though.
  6. squonk2 macrumors newbie

    Dec 5, 2014
    Thank you, GGJstudios. I appreciate your expertise!
  7. satcomer macrumors 603


    Feb 19, 2008
    The Finger Lakes Region
    Tales really consider using a free personal account at OpenDNS because you can set it up to block known Trojan hosting sites with their Phisphing Protection.
  8. Dave Braine macrumors 68040

    Dave Braine

    Mar 19, 2008
    Warrington, UK
  9. chown33 macrumors 604

    Aug 9, 2009
    It should be a Sticky Wiki. Or a Wiki Sticky.
  10. 2012Tony2012 macrumors 6502a


    Dec 2, 2012
    And what about if a person does not practise safe computing, how can that person protect themselves from getting nasties?
  11. GGJstudios macrumors Westmere


    May 16, 2008
    Antivirus apps may catch some of the malware such a user might encounter, but not all. If a user is determined to be careless about how thy use their computer, there is no method of protection that will be completely effective. Given that safe computing is not cumbersome, why wouldn't anyone choose to not practice it?
  12. 2012Tony2012 macrumors 6502a


    Dec 2, 2012
    So in other words....if someone doesn't practice "safe computing", then their Mac can indeed get infected?
  13. GGJstudios macrumors Westmere


    May 16, 2008
    It is very unlikely that an average Mac user will ever encounter malware, unless they're regularly engaging in risky activities, such as installing pirated software. It is possible, however, for any Mac to be infected if the user doesn't practice safe computing, even if they have antivirus software installed.
  14. 2012Tony2012 macrumors 6502a


    Dec 2, 2012
    #14 there are virus on Mac that someone may get if they do not practice safe computing.

    And there are Mac apps that are virus', for example pirated apps for Mac?
  15. crjackson2134 macrumors 68020


    Mar 6, 2013
    Charlotte, NC
  16. 2012Tony2012 macrumors 6502a


    Dec 2, 2012
    So not a single Virus exists for Mac?:eek:
  17. chown33 macrumors 604

    Aug 9, 2009
    This is answered in the first post.

    Read the definition of a virus by finding the "What is a virus?" heading.

    Then find the words "in the wild" and read what it says there.

    If the above doesn't answer your question, then ask a more specific question.

    If you haven't read the first post completely, then please do that before asking additional questions. There's no purpose in asking questions that are already answered.
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