I have a wordpress blog under my own domain. It does not have special security.

For the past 1 week, my blog got spammed by someone from Russia - I think the contents of my blog somehow angered him. He posts about 20 spam comments (only links to drugs, etc..) daily at staggered hours. I just can't understand. Comments need to enter name, email and also to pass a "captcha" graphics verification. It would be extremely boring and tedious to do such spamming manually. In general comments cannot be done through automated software unless some expert hack into my site.

Does anyone know if it is likely someone is able to hack into my site?