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. MALWARE TERMINOLOGY 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. ANTIVIRUS APPS 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. WHAT SECURITY STEPS SHOULD I TAKE? 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 WHAT ABOUT SENDING FILES TO WINDOWS USERS? 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.WHY AM I BEING REDIRECTED TO OTHER SITES? 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: *UPDATE - RECENT THREATS IN THE NEWS 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: New Java-Based Malware Targets Mac OS X, But Threat Level DisputedAs 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.