It is somewhat hard to comment on something that happened a few months ago as any evidence is likely to be history. There is also no malware name given for the alert or what this error no. issue was/is in relation to the alert.
The winlogon.exe file is a target for some malware where it misuses the legit file for malicious purposes.
The last thing I would have done though when getting the alerts would have been to stop the file system shield as you never know going on.