mid session new logon account?

what's up with this message?

An account was successfully logged on.

Subject:
Security ID: SYSTEM
Account Name: MAINFRAME$
Account Domain: WORKGROUP
Logon ID: 0x3e7

that happened in the middle of my morning?

and soon after, the computer froze. . .

thanks

sportsguy

nad just prior to that

A logon was attempted using explicit credentials.

Subject:
Security ID: SYSTEM
Account Name: MAINFRAME$
Account Domain: WORKGROUP
Logon ID: 0x3e7
Logon GUID: {00000000-0000-0000-0000-000000000000}

Account Whose Credentials Were Used:
Account Name: SYSTEM
Account Domain: NT AUTHORITY
Logon GUID: {00000000-0000-0000-0000-000000000000}

Target Server:
Target Server Name: localhost
Additional Information: localhost

Process Information:
Process ID: 0x2a0
Process Name: C:\Windows\System32\services.exe

Network Information:
Network Address: -
Port: -

This event is generated when a process attempts to log on an account by explicitly specifying that account’s credentials. This most commonly occurs in batch-type configurations such as scheduled tasks, or when using the RUNAS command.

is this how an antivirus or a virus user logons on?

what does this mean?

thanks

sportsguy