If you have signed up in Google Analytics, it would be easier for you to track your visitors and more statistics.
I would say that they are spammers rather than hackers. If they are hackers, they might have killed your blog a long time ago.
According to Searchmetrics study, these are the SEO Factors which Bing considers in its ranking.
(1) Top brands rank higher on Bing, as they do in Google.
(2) Backlink numbers are closely linked to higher rankings on Bing
(3) Social signals closely linked to higher rankings