Trojan removal?

Question

I am a new Mac user ( <6 months) . A fellow Mac user reccommended that I install Sophos Anti Virus, which I did and have had a few threats which have been easily removed.
     However this morning as I was reading my e-mails Sophos informed me that a threat had been detected,  "Troj/Zbot-ATN". This could not be removed by Sophos , it  told me to get instructions by going to the Sophos site to remove it manually. But they did not work.
      I then googled the said Trojan and found instructions which seemed too complicated for me to follow, but there was a link to VirusBarrierX6 which would remove it .
    It was reccommended on the Mac user site so I installed it and then did a full scan. VirusBarrier did not find the Trojan.
A couple of hours later Sophos informed me that another threat had been detected, "Mal/BredoZp-B". This was removed by Sophos , but then returned within
less than a minute.
       These threats are usually as a result of visiting dodgy websites or installing malicious software, not guilty of either.All I was doing this morning was checking e-mails and last nights football results on a site that I have benn using for the last few years.
        I went from a PC to a Mac to avoid these problems, any help much appreciated,
                                                                         thanks Paul.

Answer 1

VIRUSES
No viruses that can attack OS X have so far been detected 'in the wild', i.e. in anything other than laboratory conditions.
It is possible, however, to pass on a Windows virus to another Windows user, for example through an email attachment. To prevent this all you need is the free anti-virus utility ClamXav, which you can download for Tiger and Leopard (check with them about Lion) from:
http://www.clamxav.com/
The new version for Snow Leopard is available here:
http://www.clamxav.com/index.php?page=v2beta
Note: ClamAV adds a new user group to your Mac. That makes it a little more difficult to remove than some apps. You’ll find an uninstaller link in ClamXav’s FAQ page online.
If you are already using ClamXav: please ensure that you have installed all recent  Apple Security Updates  and that your version of ClamXav is the latest available.
Do not install Norton Anti-Virus on a Mac as it can seriously damage your operating system. Norton Anti-Virus is not compatible with Apple OS X.
FAKE ANTI-VIRUS SOFTWARE and associated MALWARE
Do not be tricked by 'scareware' that tempts computer users to download fake anti-virus software that may itself be malware.
Fake anti-virus software that infect PCs with malicious code are a growing threat, according to a study by Google. Its analysis of 240m web pages over 13 months showed that fake anti-virus programs accounted for 15% of all malicious software.
Scammers trick people into downloading programs by convincing them that their PC is infected with a virus.
Once installed, the software may steal data or force people to make a payment to register the fake product.
Beware of PDF files from unknown sources. A security firm announced that by its counting, malicious Reader documents made up 80% of all exploits at the end of 2009.:
http://www.computerworld.com/s/article/9157438/in whichRogue_PDFs_account_for_80_of_all_exploits_says_researcher
TROJANS and RE-DIRECTION TO FAKE WEBSITES
The appearance of Trojans and other malware that can possibly infect a Mac seems to be growing, but is a completely different issue to viruses.
If you allow a Trojan to be installed, the user's DNS records can be modified, redirecting incoming internet traffic through the attacker's servers, where it can be hijacked and injected with malicious websites and pornographic advertisements. The trojan also installs a watchdog process that ensures the victim's  (that's you!)  DNS records stay modified on a minute-by-minute basis.
You can read more about how, for example, the OSX/DNSChanger Trojan works (by falsely suggesting extra codecs are required for Quicktime) here:
http://www.f-secure.com/v-descs/trojan_osx_dnschanger.shtml
SecureMac has introduced a free Trojan Detection Tool for Mac OS X.  It's available here:
http://macscan.securemac.com/
First update the MacScan malware definitions before scanning. You can also contact their support team for any additional support - [email protected] [/b]
The DNSChanger Removal Tool detects and removes spyware targeting Mac OS X and allows users to check to see if the trojan has been installed on their computer; if it has, the software helps to identify and remove the offending file. After a system reboot, the users' DNS records will be repaired.
(Note that a 30 day trial version of MacScan can be downloaded free of charge from:
http://macscan.securemac.com/buy/
and this can perform a complete scan of your entire hard disk. After 30 days free trial the cost is $29.99. The full version permits you to scan selected files and folders only, as well as the entire hard disk. It will detect (and delete if you ask it to) all 'tracker cookies' that switch you to web sites you did not want to go to.
A white paper was published on the subject of Trojans by SubRosaSoft, available here:
http://www.macforensicslab.com/ProductsAndServices/index.php?main_page=document_ general_info&cPath=11&products_id=174
Also, beware of MacSweeper:
MacSweeper is malware that misleads users by exaggerating reports about spyware, adware or viruses on their computer. It is the first known "rogue" application for the Mac OS X operating system. The software was discovered by F-Secure, a Finland based computer security software company on January 17, 2008
http://en.wikipedia.org/wiki/MacSweeper
On June 23, 2008 this news reached Mac users:
http://www.theregister.co.uk/2008/06/23/mac_trojan/
More on Trojans on the Mac here:
http://www.technewsworld.com/story/63574.html?welcome=1214487119
This was published on July 25, 2008:
Attack code that exploits flaws in the net's addressing system are starting to circulate online, say security experts.
The code could be a boon to phishing gangs who redirect web users to fake bank sites and steal login details.
Net security groups say there is anecdotal evidence that small scale attacks are already happening.
Further details here:  http://news.bbc.co.uk/2/hi/technology/7525206.stm
A further development was the Koobface malware that can be picked up from Facebook (already a notorious site for malware, like many other 'social networking' sites like Twitter and MySpace etc), as reported here on December 9, 2008:
http://news.bbc.co.uk/newsbeat/hi/technology/newsid_7773000/7773340.stm
As to the recent 'Conficker furore' affecting Intel-powered computers, MacWorld recently had this to say:
http://www.macworld.co.uk/news/index.cfm?email&NewsID=25613
You can keep up to date, particularly about malware present in some downloadable pirated software, at the Securemac site:
http://www.securemac.com/
HOW TO AVOID RE-DIRECTION
Adding Open DNS codes to your Network Preferences, should give good results in terms of added security as well as speed-up:
If you are using a single computer: Open System Preferences/Network. Double click on your connection type, or select it in the drop-down menu, and in the box marked 'DNS Servers' add the following two numbers:
208.67.222.222
208.67.220.220
(You can also enter them if you click on Advanced and then DNS)
Sometimes reversing the order of the DNS numbers can be beneficial in cases where there is a long delay before web pages start to load, and then suddenly load at normal speed:
http://support.apple.com/kb/TS2296
If your computer is part of a network: please refer to this page: http://www.opendns.com/start/best_practices/#your_network and follow the advice given.
There may be other ways of guarding against Trojans, viruses and general malware affecting the Mac, and alternatives will probably appear in the future. In the meantime the advice is: be careful where you go on the web and what you download!
WHAT TO DO IF YOU THINK YOUR MAC HAS BECOME 'INFECTED':
If you think you may have acquired a Trojan, and you know its name, you can also locate it via the Terminal:
http://theappleblog.com/2009/04/24/mac-botnet-how-to-ensure-you-are-not-part-of- the-problem/
Although any content that you download has the possibility of containing malicious software, practising a bit of care will generally keep you free from the consequences of anything like the DNSChanger trojan.
1. Avoid going to suspect and untrusted Web sites, especially p'orn'ography sites.
2. Check out what you are downloading. Mac OS X asks you for you administrator password to install applications for a reason! Only download media and applications from well-known and trusted Web sites. If you think you may have downloaded suspicious files, read the installer packages and make sure they are legit. If you cannot determine if the program you downloaded is infected, do a quick Internet search and see if any other users reported issues after installing a particular program. A recent example is of malware distributed through innocent looking free screensavers:  http://www.zdnet.com/blog/security/malware-watch-free-mac-os-x-screensavers-bund led-with-spyware/6560?tag=nl.e589
3. Use an antivirus program like ClamXav. If you are in the habit of downloading a lot of media and other files, it may be well worth your while to run those files through this AV application.
4. Use Mac OS X's built-in Firewalls and other security features.
5. LimeWire (now defunct) and other peer-to-peer sharing applications and download torrents supplying pirated software, movies etc are hotbeds of potential software issues waiting to happen to your Mac. Everything from changing permissions to downloading trojans and other malicious software can be acquired from using these applications. Similar risks apply to using Facebook, Twitter, MySpace, YouTube and similar sites which are prone to malicious hacking:  http://news.bbc.co.uk/1/hi/technology/8420233.stm
6. Resist the temptation to download pirated software. After the release of iWork '09, a Trojan was discovered circulating in pirated copies of Apple's productivity suite of applications (as well as pirated copies of Adobe's Photoshop CS4). Security professionals now believe that the botnet (from iServices) has become active. Although the potential damage range is projected to be minimal, an estimated 20,000 copies of the Trojan were downloaded.  SecureMac offer a simple and free tool for the removal of the iBotNet Trojan available here:
http://macscan.securemac.com/files/iServicesTrojanRemovalTool.dmg
YOUR PRIVACY ON THE INTERNET and the latest risks to look out for:
There is the potential for having your entire email contact list stolen for use for spamming:
http://www.nytimes.com/2009/06/20/technology/internet/20shortcuts.html?_r=1
NOTE: Snow Leopard, OS 10.6.x, offers additional security to that of previous versions of OS X, but not to the extent that you should ignore the foregoing:
http://www.apple.com/macosx/security/
Apple's 10.6.4 operating system upgrade silently updated the malware protection built into Mac OS X to protect against a backdoor Trojan horse that can allow hackers to gain remote control over your treasured iMac or MacBook.
http://www.sophos.com/blogs/gc/g/2010/06/18/apple-secretly-updates
And if you are using iPhone Apps you are also at risk of losing all privacy:
http://www.engadget.com/2010/10/03/hacker-claims-third-party-iphone-apps-can-tra nsmit-udid-pose-se/
The advent of HTML5  may also be a future threat to internet privacy:
http://www.nytimes.com/2010/10/11/business/media/11privacy.html?_r=1&hp
Security of OS X generally:
http://www.apple.com/macosx/security/
http://www.nsa.gov/ia/_files/os/applemac/I731-007R-2007.pdf
Security Configuration for OS Version 10.5 Leopard:
http://images.apple.com/server/macosx/docs/Leopard_Security_Config_2nd_Ed.pdf