How do I block access to my blog from "xxxxxxx.com"?or
I am looking at a lot of traffic from "xxxxxxx.com". Am I being hacked?as if everybody visiting the blog should be suspected of having nefarious intent.
When you see an entry in your visitor log, it (with a few exceptions) represents a person, who clicked on a link somewhere (possibly in a search hit list, or on another blog or website), and landed on your blog.
If you have a public blog, this is to your benefit. More clicks on links to your blog leads to more traffic to your blog, which leads to increased search engine reputation, and to still more traffic to your blog. The other website is not stealing anything from you. If you control or monitor your backlinks, your blog won't have any links to any unknown websites. If you control access to your visitor logs, your readers won't know or care that odd visitors are accessing your blog, after having previously accessed an unknown or "unsuitable" blog or website.
It is possible, within limits, to restrict access to your blog - but what do you gain, by doing that? Google does not limit traffic by volume, nor do they charge you extra. Enjoy the attention. Spend your time publishing to the blog, and working on the blog.