Event 4625 windows security auditing failed to logon. Failure reason:unknown user name or bad password

I have Windows server 2012 R2 azure virtual instance and few ports are open on it i.e. (80,443,RDC). I have observed the below logs into windows event viewer in security section.

Event 4625 : Microsoft windows security auditing

-------log description start
An account failed to log on.

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

Logon Type: 3

Account For Which Logon Failed:
Security ID: NULL SID
Account Name: ALLISON
Account Domain:

Failure Information:
Failure Reason: Unknown user name or bad password.
Status: 0xC000006D
Sub Status: 0xC0000064

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

Network Information:
Workstation Name:
Source Network Address: -
Source Port: -

Detailed Authentication Information:
Logon Process: NtLmSsp
Authentication Package: NTLM
Transited Services: -
Package Name (NTLM only): -
Key Length: 0

This event is generated when a logon request fails. It is generated on the computer where access was attempted.

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 was requested. The most common types are 2 (interactive) and 3 (network).

The Process Information fields indicate which account and process on the system requested the logon.

The Network Information 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.
- 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.

-------log description end

The logs are continuously generating in event viewer (3-4 request per second) and account name always changes as mention below.

Account For Which Logon Failed:
Security ID: NULL SID
Account Name: ATCNSBAYFG
Account For Which Logon Failed:
Security ID: NULL SID
Account Name: SUPPORT
Account For Which Logon Failed:
Security ID: NULL SID
Account Name: SUPPORT
Account For Which Logon Failed:
Security ID: NULL SID
Account Name: HAYLEY
Account For Which Logon Failed:
Security ID: NULL SID
Account Name: TEST5
and more...

What I have tried:

<pre>What I tried:
1. Disabled the all open ports from azure portal even RDC.
2. Disabled the Windows Essentials services.
3. Disabled Alert Evaluations task from windows scheduler.

but still the logs are generating in event viewer. Is this windows attacked or some thing else? and how to prevent this?