There have been several scams involving sites that promises free voucher codes, credits and even a voting site for Habbos.
For instance, someone might give you a website link to vote for other Habbos/ Fansites and it will eventually ask you to enter your Habbo email ID password to vote for them. Never enter your Habbo email ID to any site apart from www.habbo.com or you risk getting your Habbo account compromised. Another scam involved getting free credits by dragging a picture/ website link to your browser tool bar.
For the safety of your account, wise up to scamsites promising you the moon, only for you to find that by entering the site you have inadvertently installed a keylogger or trojan horse virus on your computer. As a general rule, don't open third-party links given out on Habbo, as you never know what may lurk on those sites.