A computer hacker managed to breach an employment agency's online security and accessed the personal details and bank account numbers of 8,000 temps.
West Midlands Police were called to investigate after Warwick University's Unitemps service was compromised.
The hacker, who took extensive measures to avoid detection, found CVs and in some cases photographs in the system.
The information was deleted, but it is feared the files were copied and could now be used to obtain credit illegally.
The details were held by the Unitemps service, which is used by the university to help students and former students to find work.
As it is not clear whether the offender copied the temps' details before deleting them, the university has written to all those registered on the site informing them of a "malicious external assault" on the system.
Susannah Rees, whose personal details were on the database, told BBC Radio 4's You and Yours programme that she felt uncomfortable knowing someone could pretend to be her.
Ms Rees, from the Wirral, said: "The implications are not good. Some of the information could be used to obtain credit.
"You had your photograph, bank account, address, probably your CV, and where you worked.
"It's quite a lot isn't it for someone to be able to pretend to be you? It's pretty uncomfortable, not nice."
In a statement, Unitemps said: "Even though there is no indication that the attacker's actions went beyond an intent deliberately to damage the system, it is impossible to tell whether the data was simply deleted or whether a copy was also taken.
"Therefore, as soon as contact details were recovered, Unitemps took the precaution of attempting to contact everyone whose private information could have been put at risk by this attack to inform them of the situation."
The website has been closed down while steps are taken to improve security and the West Midlands Police investigation is continuing.