Many successful logon and logoff requests in Windows Event Viewer

Question

I'm getting thousands of logon and logoff requests every day from the same computer in the local network. It seems the computer is connecting from a different port every time.

What could be the cause of this and is it dangerous?

Both computers are using Windows 7 Pro SP1.

An example of the event log:

An account was successfully logged on.

Subject:
    Security ID:        NULL SID
    Account Name:       -
    Account Domain:     -
    Logon ID:       0x0

Logon Type:         3

New Logon:
    Security ID:        ANONYMOUS LOGON
    Account Name:       ANONYMOUS LOGON
    Account Domain:     NT AUTHORITY
    Logon ID:       0x77f9286b
    Logon GUID:     {00000000-0000-0000-0000-000000000000}

Process Information:
    Process ID:     0x0
    Process Name:       -

Network Information:
    Workstation Name:   <name>
    Source Network Address: <ip>
    Source Port:        5436

Detailed Authentication Information:
    Logon Process:      NtLmSsp 
    Authentication Package: NTLM
    Transited Services: -
    Package Name (NTLM only):   NTLM V1
    Key Length:     128

This event is generated when a logon session is created. It is generated on the computer that was accessed.

The subject fields indicate the account on the local system which requested the logon. This is most commonly a service such as the Server service, or a local process such as Winlogon.exe or Services.exe.

The logon type field indicates the kind of logon that occurred. The most common types are 2 (interactive) and 3 (network).

The New Logon fields indicate the account for whom the new logon was created, i.e. the account that was logged on.

The network fields indicate where a remote logon request originated. Workstation name is not always available and may be left blank in some cases.

The authentication information fields provide detailed information about this specific logon request.
    - Logon GUID is a unique identifier that can be used to correlate this event with a KDC event.
    - Transited services indicate which intermediate services have participated in this logon request.
    - Package name indicates which sub-protocol was used among the NTLM protocols.
    - Key length indicates the length of the generated session key. This will be 0 if no session key was requested.

Answer 1

I hate these anon login records. They're nothing to worry about. Here are the details, and a link to the full article which also details how to disable them.

• Event 4624 null sid is the valid event but not the actual user's logon event.
• The reason for the no network information is it is just local system activity. Windows talking to itself.
• The "anonymous" logon has been part of Windows domains for a long time--in short, it is the permission that allows other computers to find yours in the Network Neighborhood

http://www.morgantechspace.com/2013/10/event-4624-null-sid-repeated-security.html