htaccess problem

I have a problem where my htaccess file keeps getting hijacked. It started this week, and I don't know whether is it a rouge plugin or someone able to hack the account. I do know I have been sitting on the account watching it happening.

It is hacking it to redirect everything to a spam site in Russia. I have the chmod set to 444 on .htaccess, and whatever is changing it is still capable of doing do. Any ideas on what I should be doing next? It is throwing .htaccess files into a number of different directories, and other random files for viagra and "You have been sent here because a friend recommended you" html and php pages, also in multiple subdirectories.