Input source language keeps changing on Mac OS X 10.9.4

First time posting on this site so hopefully I am posting it in the right place. Apologies if not. I've been having issues with my MacBook Pro (15-inch, mid 2009). I have my input source language set as "Irish"; however, as of today any time I log in (after the computer has been shut down) the input source language has switched itself to "U.S.", and I have to go and change it back to "Irish".

I haven't changed anything major as of late. The only thing I can think of is that I accidently clicked a link in a spam email which linked to a "Linkbucks" site which then had a "skip this ad" button which again I foolishly clicked which in turn led to a JPG image of someone's Facebook. I googled "Linkbucks" and read that it is a web browser hijacker virus which can then change your settings etc.

I ran Clamx Av to see if anything of that sort was on my computer, but nothing came up. Am I just being paranoid here thinking some Linkbucks virus has infected my computer? How do I stop the computer from constantly resetting the input language on power-off? Any help would be much appreciated.