Haddonfield Memorial High School officials say the students used a special program to capture usernames and passwords from anyone who used certain computers at the school.
The Camden County Prosecutor's Office says the students accessed over 200 of the school's 2,000 accounts.
The breach into Haddonfield High School's computer system was going on for up to two months.
Haddonfield School District officials say several students installed a keystroke logging program that enabled them to acquire names and passwords of anyone using the rigged computers; that included students and faculty. Authorities say grades were altered.
"There is a possibility of that. What we do know also is that our backup systems, we being able to go back and look at all the grades that students had originally entered. All that information has been corrected at this point," superintendent Alan Fegley said.
The case involving the unidentified students is under investigation by local police and the county prosecutor's computer experts and juvenile unit.
In an e-mail to parents, the school's principal said, 'We are confident we have identified the students and built in the appropriate controls to restrict their activity and that of anyone else who may foster a similar plan.'
"I think the school's handling it well; I certainly think there should be consequences," parent Jane Grabowski.
Students and parents have been told to change passwords on school related accounts and even home accounts if they use the same password.
"It's a nuisance, you have to change everything," junior Jordan Harris said.
Authorities found out about the breach on Tuesday when a staff member saw a student trying to access something he should not have.
Students have been suspended pending the outcome of the investigation and they could face criminal charges.