Are Mac users subject to the DNSChanger malware

The DNSChanger malware was addressed by Apple a long time ago, so your MBA is not likely to be affected.

Go here to be sure: http://www.dns-ok.us/

You should get this

If you are not in the US check here for an appropriate site:

https://forms.fbi.gov/check-to-see-if-your-computer-is-using-rogue-DNS

They can be, check the English link at this site.

http://www.dcwg.org/detect/