Safari is.. Totally Freaking Out

Question

Alright, so, long time user here, and I'm experiencing a strange problem with Safari. I've done a bit to try and remedy it, but to no avail. I've had a few friends log onto their various Twitter, Facebook, etc accounts on my computer. Being the confidential friends they are, they are sure not to check "remember my password" or whatever.
Well, occasionally, I reload my while logged into my Twitter or Facebook, only to find that I am now on one of my friends accounts, without any explanation or anything. I mean, I was literally sitting there, wondering, "Oh, I wonder if anything new has happened here in the endless abyss of the internet," so I click refresh and suddenly I am on an entirely different account that I shouldn't have access to. The only connection is that the account I now find myself on was once or twice logged in to from my computer, and a long time ago at that. And like I said, I know they haven't clicked "remember my password," and even if they did, shouldn't resetting Safari and emptying the cache.. remove that all?
It has happened multiple times on different websites.. But it's kinda starting to bug me. If nothing else, it's a huge security breach thing- If I wasn't a respectful sort of person, I would have had several opportunities to mess with accounts I shouldn't have access to.
I've reset Safari multiple times and emptied the cache as well. After that, I thought the problem was gone, but it resurfaced tonight. Suggestions? I was thinking about moving to the preference file or something, but I don't want to lose that if I don't have to.

Answer 1

Twitter? Facebook? The two best-known sources for malware!
You may have acquired a Trojan. Please read on:
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 from:
http://www.clamxav.com/
However, 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.
SecureMac has introduced a free Trojan Detection Tool for Mac OS X. It's available here:
http://macscan.securemac.com/
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 the cost is $29.99. The full version permits you to scan selected files and folders only, as well as the entire hard disk.)
A white paper has recently been published on the subject of Trojans by SubRosaSoft, available here:
http://www.macforensicslab.com/ProductsAndServices/index.php?mainpage=document_general_info&cPath=11&productsid=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 information on Mac security can be found here:
http://macscan.securemac.com/
The MacScan application can be downloaded from here:
http://macscan.securemac.com/buy/
You can download a 30 day trail copy which enables you to do a full scan of your hard disk. After that it costs $29.95.
More on Trojans on the Mac here:
http://www.technewsworld.com/story/63574.html?welcome=1214487119
The latest news on the subject, from July 25, 2008, is:
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.
In light of the news net firms are being urged to apply a fix for the loop-hole before attacks by hi-tech criminals become widespread.
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 recent development is the Koobface malware that can be picked up from Facebook (already a notorious site for malware), as reported here on December 9, 2008:
http://news.bbc.co.uk/newsbeat/hi/technology/newsid_7773000/7773340.stm
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!