hacked server

How can you find out if your server was hacked?

Here are some of the symptom if your site is hacked;
-Strange files on your server
-Drop in Google Search Engine Results Rank
-A Red Warning Alert in Google Chrome or Firefox
-Change in “.htaccess” file
-Google Indexes Your Site with strange keywords ex;Pharmacy/Adult Text
-Change in site code or even on layout

I'm pretty sure you will understand easily from the unusual activities and files, password changes etc. , if someone hacks your server. :)