At least 4800 Australian websites have been lost with no chance of recovery following a break-in at Australian domain registrar and web host Distribute.IT.

The hack attack caused so much damage that four of the company's servers were "unrecoverable", the company said, leaving thousands of website owners in the lurch.

"The overall magnitude of the tragedy and the loss of our information and yours is simply incalculable; and we are distressed by the actions of the parties responsible for this reprehensible act," Distribute.IT said.

As reported by Fairfax Media last week, Distribute.IT was hit with a "deliberate, premeditated and targeted attack" on its servers last Saturday but it is still struggling to work out exactly what happened or how much data was stolen.

Security experts warned that thousands of websites were vulnerable to being hijacked and extensive private data were at risk of being stolen.