Rewrite Rules Disappeared from Htaccess file

Hey Guys

Something really really strange happened to my main site ThinkTaiwan.com. It has been up and running for 3 years now.

All of a sudden without me making any changes to core files, all links returned a 404 not found page except for the main index page and the wordpress backend. Those worked fine but pages and posts all were broken links.

Messed around with permalinks and that didn't fix it however the default ones worked. I googled and found that I should add rewrite rules to htaccess. But I thought how silly it would be for me to have to do this since I have done this before and the site has been running for 3 years.

But guess what? I open up my htaccess file to find that every Wordpress rule was GONE! Adding back the neccessary rewrite rules fixed my broken links.

My question to everyone is, how in the world would these rules ever get erased from the htaccess file without it manually being erased by myself? Thanks!