Fake registrations

my blog run only a week but i already have many random users (mostly with yahoo and maildin.com emails). Now, im pretty new to all that stuff and don’t know how to recognize bot users… but obviously these are not real people because my site has 0% popularity and only 3 posts.

how these users come to the site, how i need to recognize between them to real people, and how to prevented that??

tnx 🙂