Be careful when downloading software.
Make sure to download only from official sources:
Official Groestlcoin Clients for Win, Mac, Linux
Simple Machines wants to thank everyone who helped make SMF 2.1 what it is today; shaping and directing our project, all through the thick and the thin. It wouldn't have been possible without you. This includes our users and especially Charter Members - thanks for installing and using our software as well as providing valuable feedback, bug reports, and opinions.
And for anyone we may have missed, thank you!