sorry about your luck on this adventure. though i must inquire, how is it that there are reportedly over 100K registered users on boonex unity and your site is the only one getting 'hacked' as you call it.
as an IT specialist, and systems administrator for over 300 dolphin sites, i can tell you the issue is not and i repeat, not with dolphin.
you reference the word 'hacked' though you provide no access logs, or any further information to go on. your hosting company should be able to provide you with a log of all access to your server.
let's consider exactly what might be happening, your server is not secure, therefore, ftp is not secure, and i would bet that FTP is the means of access.
the irony of repeatedly being accessed leads me to believe that there are other underlying issues, that are not being reported.
so in your quest for assistance, you must also provide relative information to the exact problem.
a couple of questions that can be answered:
1. after the first time you realized you had this problem, did you change all login parameters on the site, the database, and your hosting account?
2. which ftp client are you using?
3. what version of dolphin are you running?
4. have you asked your hosting provider for access logs to the server account?
5. have you given your login credentials out to anyone?
i personally dont think this is a dolphin problem. i am running way too many dolphin sites to even consider this to be an issue with dolphin.
When a GIG is not enough --> Terabyte Dolphin Technical Support - Server Management and Support