i wouldnt worry
although a quick way to find some malware specific to your operating system is to search about what kind of malware your OS is vulnerable to, i wouldnt worry unless i was a version of windows;
there have been very few, if not none, exploits that didnt require you to type your admin passwd;
other than that, i would worry more about someone sniffing the traffic that your wireless access point sends out;
especially if you live in an area that is densely populated;
you just need to go to your routers homepage, open a browser with firefox while plugged into your router, type 192.168.1.1 in the browser bar,
you should see a screen that asks for username and passwd,
check your routers manual or google, but they are usually "admin" for the username (no quotations) and "password" "passwd" or "admin" for the password (no quotations),
so then you are at your router config page, change the password, and take some time to read the settings,
make sure you are using WPA or WPA2 security,
this is the service that asks for a password when you connect to your network, make sure the password is a bunch of upper and lower case symbols and numbers and letters, like "ghiYYR@%mycomp" would be a good password,
why?
your password is cracked by computers that sit near your access point and gather data, then use that data in a password cracker that goes through iterations of symbols, commonly using all the words in a dictionary for starters, so "apple" would probably be an easy to crack password;
i wouldnt worry, your mac is EXTREMELY secure, so is your linux!^_^