You have probably heard the terms “viruses, trojans and worms,” which are all under the umbrella term for malicious software called malware. These items are usually thought of as interchangeable or the same thing. Although they are similar in that they are created with malicious intent, if you understand the differences, you will better be able to better understand the threat so you can protect your Mac.
Like a virus that infects people, a computer virus seeks to replicate itself and spread to another host to repeat the process. Since they need execute and write permissions for this, viruses attach themselves to programs (sometimes legitimate) so that when you open the host program the virus is also activated. There are a couple of subclasses of viruses, but they have the same basic characteristics.
A worm is very similar to a virus, but it can travel between other computers or devices without interaction from any user. Also unlike a virus, a worm does not need to attach itself to an existing program. One of the most famous worms was Stuxnet. Stuxnet was created by a unknown source and its main target was a nuclear power facility in Iran. It could spread from a computer to a flash drive and then to a phone and back to a computer (and so on) until it found its target. Even though this is the most advanced worm to date, a common malicious computer worm can do the same traveling to infect machines.
The word trojan rises from the way this type of malware works. Similar to Greek mythology, the user is tricked into installing the trojan horse which is often disguised as friendly software. The effect of a trojan horse can vary, depending on the creator’s intention. The most recent well-known trojan for the Mac is “Flashback,” which disguised itself as an Adobe Flash Player update. Once installed, it would be able to collect user data and passwords and make them accessible to the creator of the trojan. It could also set up a BotNet which is a network of computers to attack other machines and services.
So what does this mean for us as Mac users? It has long been one of the points in the Windows/Mac debate that Macs are immune to viruses and malware. It would be more true to say that there are currently no virus threats to Macs. As far as other forms of malware, we have all seen that certainly any machine can be a victim. Certainly though, as Mac users we only deal with a small fraction of the headaches that Windows users have with this problem.
The bottom line is to both be careful and pragmatic — as time goes on, the number of threats is guaranteed to rise. Use a malware program — either one of the paid options, such as Norton or MacAfee, or one of the free utilities out there that performs well and seems to have minimal impact on system performance such as Sophos and Clam XAV.