Symantec Endpoint Protection (SEP) client for Windows has one or more definition issues, such as:
Definitions fail to update
Definition information in the Windows registry is different from the information in the usage.dat file
Duplicate product definition entries in the usage.dat file
The usage.dat product entries uses different definitions
Note: To quickly check if this issue still exists or has been resolved on the computer, download and run SymDiag.
Corruption of virus definitions may have many causes. Consider these questions when responding to potentially corrupted content definitions:
Is the corruption believed to be a one-time issue with a suspected one-time cause?
Is the corruption a recurring issue due to an unknown cause?
Known, one-time cause
If the known or suspected cause is not anticipated to recur, you can clear corrupted definitions by uninstalling and reinstalling SEP. Alternately, you can manually clear definitions as explained in the following article: