Volume Number: 27
Issue Number: 01
Column Tag: Real World Review

Real World Review: Sophos Anti-Virus for Mac, Home Edition

Enterprise-grade antivirus software, now free for home Macs

by Joshua Long

Businesses are often required by laws and company policies to run antivirus software on all their computers, Macs included. In the home environment, however, there are no such requirements, and Mac users have debated for years about whether they should go to the trouble of running antivirus software. Is it really worthwhile to spend $40 every year to protect a Mac with commercial-grade antivirus software, or to endure the agonizing speed degradation commonly associated with AV? Thanks to Sophos, home users can now have quality protection without these frustrations.

Enterprise antivirus maker Sophos announced in November that they would begin offering a free Home Edition of Sophos Anti-Virus to all Mac users. The announcement came just one week after SecureMac and Intego had independently published information about new Java-based Mac malware spreading through Facebook and other sites, dubbed Boonana by SecureMac and identified as a variant of the Koobface malware by Intego.

Two weeks after the release of Sophos Anti-Virus for Mac Home Edition, Sophos released a report showing that a significant number of Macs running their software had been infected with malware. This malware included both Mac-native threats as well as plenty of Java-based malware, which Sophos pointed out "could easily be adapted to download Mac-based threats," as was the case with Boonana. Two Mac-specific threats, OSX/Jahlav-C and OSX/DNSCha-E, were each found on about 1 in every 100 Macs scanned. (For the full Sophos report, see http://macte.ch/sophos_stats).

Sophos' antivirus engine is one of the best on the market. In AV-Comparatives' (av-comparatives.org) November 2010 tests of proactive detection of new malware, Sophos Anti-Virus ranked in the top three PC antivirus products, earning the highest certification level (Advanced+). The tests also took into consideration the number of false positives, of which the Sophos engine had "few."

Let's take a look at how Sophos Anti-Virus Home Edition compares to other free alternatives for the Mac. The two most prominent freeware antivirus solutions are ClamXav (clamxav.com) and PC Tools iAntiVirus (iantivirus.com), and each is very different from Sophos.

ClamXav is free for anyone to use in any environment, from home computers to enterprise workstations. Although ClamXav does not provide on-access scanning of the whole computer, it can be manually configured to scan files that are downloaded or copied to specific folders, for example ~/Downloads and ~/Desktop. Like Sophos, ClamXav detects malware designed for any platform, as opposed to Mac-only malware.

PC Tools iAntiVirus is only free for home use, and although it does offer on-access scanning, it only detects Mac-specific malware. Neither ClamXav nor iAntiVirus is a comprehensive solution compared to Sophos. Of the three, only Sophos will detect infected Web pages and e-mail attachments as soon as they are downloaded, regardless of the threat's target platform.

I tested Sophos and ClamXav with several hundred samples that I've collected from infected computers, Web sites, and e-mails over the past couple years. ClamXav only detected about 75% as many files as Sophos, although ClamXav detected some files (particularly Windows adware) that Sophos did not detect. Neither one detected all the samples, which was expected; no antivirus solution detects 100% of infected or potentially dangerous files.

Figure 1 - Threat detected by Sophos Anti-Virus

Unlike most full-featured antivirus solutions, the default settings of Sophos Anti-Virus do not automatically delete infected files or prompt users to do so. Instead, Sophos displays an alert informing the user that a threat has been detected, with options to open the Quarantine Manager or close the dialog box, and the latter is the default selection. Regardless of which option the user chooses, as long as Sophos' on-access scanner is enabled, the file is inaccessible and cannot be opened or even duplicated in the Finder or the Terminal (even using sudo).

Figure 2 - When a threat is found, Sophos denies access by default

If a malicious Mac application is detected by Sophos, attempting to open the application will result in two Mac OS X dialog boxes informing the user that they can't open the application because it is "not supported on this type of Mac." Thus, Sophos effectively quarantines the files in place.

Figure 3 - Malware is not supported on this type of Mac

Even trying to access quarantined files from another computer via a network share proves fruitless. I had Sophos running on an iMac and no antivirus software on a MacBook Pro. From the MacBook Pro I connected to an AFP share on the iMac and tried to copy a file from the iMac to the local hard drive. This resulted in a Mac OS X dialog box explaining that I did not have permission to access the file. I also tried to duplicate an infected file in-place on the network share, which caused the MacBook Pro's Finder to crash and relaunch (note to self: file a bug report). In any case, Sophos quarantines files on the local system in such a way that they cannot be accessed by remote systems.

One strange and annoying issue I've encountered is that Sophos Anti-Virus frequently grays out the Clean Up Threat button for items that should be easy for Sophos to delete on its own. For example, the action available for dealing with .zip files downloaded from parcel scam e-mails is Clean up manually, meaning that users must try to locate the infected files on their computer. This may or may not be easy, depending on whether the full path is shown in the Quarantine Manager; if the path or file name is too long, the path will be truncated, so you may have to use Spotlight or a third-party search utility to locate the file (refer to the screenshot of the Quarantine Manager). You cannot resize the window so there is no way to see the full path, and there is no Show in Finder option either.

Figure 4 - "Clean up manually"... okay, so what's the full path?

In other cases, instead of Clean up manually the available action will be Restart Mac instead, even when there's absolutely no reason why that should be necessary. I came across this after downloading fake ActiveX video codec malware, which consisted of nothing more than Windows .exe files. Why on earth would Sophos need to restart the computer to clean Windows executables that aren't in use? Worse still, restarting your Mac won't even clean up the threat; it will still be there in the Quarantine Manager after restarting.

Fortunately, Sophos did not gray out the Clean Up Threat button for the Mac OS X-specific threat I had it scan (a dangerous Space Invaders-style game called lose/lose which deletes files in the user's home directory when you destroy enemy spaceships); no manual deletion or restarting is required to clean that Mac-native threat.

Antivirus suites have a reputation of slowing down computers. In my testing, there was no noticeable decrease in system speed or usability after installing the Sophos software. I even tested it on a low-end Hackintosh netbook (a Dell Mini 10v with a 1.6 GHz Intel Atom processor and 1 GB RAM) and the system was still quite usable after installing Sophos.

For those who support Macs in a home environment, I recommend trying Sophos Anti-Virus for Mac Home Edition. Although there's currently only a small amount of Mac-specific malware in the wild, Sophos can protect Macs from other threats such as malicious JavaScript redirectors, Adobe Flash files that exploit known vulnerabilities (see Mike Hjörleifsson's CoreSec column in the MacTech November 2010 issue), multiplatform Java-based attacks like Boonana, and Windows-based malware that could accidentally be opened in a virtual environment like Parallels or VMware, and it can also discover infections on USB flash drives that you might have picked up from an infected PC unbeknownst to you.

It's time for us to put away our Smug Virus-Free Mac User shirts of yore and become more proactive at defending Macs from security threats. Three cheers to Sophos for lighting the way into battle.

Joshua Long has a master’s degree in IT concentrating in Internet Security, is a Security+ certified professional, and is currently earning a Ph.D. in Business Administration specializing in Computer and Information Security. Josh writes about malware and other information security topics at security.thejoshmeister.com. He is also the producer and host of MacTech Magazine’s official podcast, MacTech Live (www.mactech.com/live). You can follow him on Twitter @theJoshMeister or contact him via e-mail at jlong@mactech.com.