File is writable by others please fix permissions and try again

Our company have installed the 1.7 version of Community version at JustHost servers. Now we recieve this message “File is writable by others, please fix permissions and try again.” on an empty white screen, when trying to enter the backoffice / System / Magento Connect Manager - (to install new addons). I have looked thru the ftp and folder/files-settings and changed the folders (and files) in app/etc, var and media to 755 setting. I havent found anything about this problem elsewhere, and I am not sure where to look next. Any Ideas?? Thx a lot for any help!