roguinrireki de huseiakusesu wo kakuninsuru.

Here で shows the means/source/context used to check something.

So ログイン履歴で不正アクセスを確認する means something like:

• check for unauthorized access using the login history
• confirm unauthorized access from the login history
• look in the login history to verify unauthorized access

It is not the direct object of the verb. The direct object is 不正アクセス.

Because 確認する is being used as a transitive verb here, and を marks what is being checked or confirmed.

So the structure is:

• ログイン履歴で = by means of / in the login history
• 不正アクセスを = unauthorized access as the thing being checked
• 確認する = to confirm / check

In natural English, we often say check the login history for unauthorized access, but Japanese is structured more like confirm unauthorized access by using the login history.

It can suggest both, and that is normal.

In this sentence, で implies:

• using the login history as evidence/material
• looking within the login history

So the nuance is somewhere between:

• in the login history
• by means of the login history
• from the login history

Japanese often leaves this kind of distinction less sharply separated than English does.

The dictionary form is often used in Japanese for:

• headings
• instructions
• labels in manuals
• general statements
• action items

So ログイン履歴で不正アクセスを確認する can sound like:

• a manual instruction
• a checklist item
• a menu description
• a general action: Check for unauthorized access in the login history

It does not automatically mean present tense in the same way English does. It often has a neutral, general, or instructional feeling.

Yes. Japanese often omits the subject when it is obvious from context.

This sentence does not say who is doing the checking. Depending on context, it could mean:

• You should check...
• The user checks...
• An administrator checks...
• We check...

In English, we usually need to supply a subject, but in Japanese it is often left unstated.

Yes, but the meaning changes.

• ログイン履歴を確認する = check the login history
• ログイン履歴で不正アクセスを確認する = check for unauthorized access by using the login history

So:

• with を, ログイン履歴 is the thing being checked
• with で, ログイン履歴 is the tool/source/place used for checking

Both are natural, but they focus on different things.

Sometimes yes, but the nuance changes.

• ログイン履歴で不正アクセスを確認する
  = confirm unauthorized access using / in the login history

• ログイン履歴から不正アクセスを確認する
  = confirm unauthorized access from the login history

から emphasizes the idea that the conclusion is drawn from that source.
で is broader and often sounds more like using it as the means/place for checking.

Both can be understandable, but で works well in an instruction-like sentence.

不正アクセス is a noun meaning unauthorized access or illegal access.

Breakdown:

• 不正 = improper, illegal, unjust, unauthorized
• アクセス = access

Together they form a compound noun. In this sentence, that noun is marked by を and acts as the object of 確認する.

You may also see related expressions like:

• 不正ログイン = unauthorized login
• 不審なアクセス = suspicious access

Because they come from different kinds of vocabulary.

• ログイン and アクセス are loanwords, so they are written in katakana
• 履歴, 不正, and 確認 are standard Sino-Japanese words, so they are usually written in kanji

This mixture is very common in technical Japanese.

Normally, standard Japanese is written without spaces:

ログイン履歴で不正アクセスを確認する。

Spaces are often added only in learning materials to make the structure easier to see. They are not part of normal Japanese writing.

Yes, it is understandable and fairly natural, especially in a technical or instructional context.

That said, depending on the exact situation, Japanese might also use slightly more explicit versions such as:

• ログイン履歴を確認する。
  = Check the login history.

• ログイン履歴で不正アクセスがないか確認する。
  = Check the login history to see whether there has been unauthorized access.

• ログイン履歴から不正アクセスの有無を確認する。
  = Confirm whether unauthorized access exists from the login history.

Your original sentence is concise and has a manual-like feel.

It could, and that version is a little more explicit.

Compare:

• 不正アクセスを確認する
  = confirm/check unauthorized access

• 不正アクセスがあるか確認する
  = check whether there is unauthorized access

The original is more compact and slightly more formal/technical in style.
The があるか version spells out the idea of whether it exists more clearly.