Good news! I've managed to take back my Steam-account, thanks to the help from the Support. The only damage this Russian ruffian seem to have done so far is removing all of my pals from the Friends-list and changed the name to "Vezus." What a peculiar name.
Anyways, the issue has been solved. I've changed back my personal information and thoroughly secured my account with Steam Guard Authenticator. So that is done.
Now I just need to seek out my friends and add them back to my Friends-list.
Thank you all for the concern during this hardship. You guys are great. Let this also be a lesson for you; always ensure that you've updated your security of your Steam-account or this hacking attempt will happen to you as well.