#12 - Aug. 20, 2010, 7:03 p.m.
Yes, Thadaim, the whisper you received was in fact a phishing whisper.
As your fellow players have mentioned, if you did go to the website in question, you may wish to thoroughly scan your computer for keyloggers, Trojans, and viruses.
You may also find this support article helpful if you come across this issue in the future:
I received an in-game whisper telling me to visit a website to claim a free reward. Is this a scam?
http://us.blizzard.com/support/article/30829