husinna roguin wo musisi, akaunto no nottori ga okori kanenai.

Because 不審 is a na-adjective when it modifies a noun.

• 不審なログイン = a suspicious login
• 不審のログイン would be unnatural here

Many words of this type take な before a noun:

• 危険なサイト = a dangerous site
• 不自然な日本語 = unnatural Japanese
• 不審なアクセス = suspicious access

So 不審なログイン is the normal way to say suspicious login.

無視し is the masu-stem of 無視する, used here in a written, connective way.

• 無視する = to ignore
• 無視し、... = ignoring ..., if one ignores ..., or and then ignores ...

In this sentence, it connects to the second part and implies a consequence:

• 不審なログインを無視し、アカウントの乗っ取りが起こりかねない。
• If suspicious logins are ignored, account takeover may occur.

This kind of verb-stem + comma is common in formal writing, notices, and warnings.

The comma helps separate the two parts of the sentence and makes the warning easier to read.

It divides:

1. 不審なログインを無視し = ignoring suspicious logins
2. アカウントの乗っ取りが起こりかねない = account takeover may occur

Japanese commas often mark pauses or clause boundaries more freely than English punctuation does. In formal written Japanese, this is very common.

Here, 乗っ取り is a noun meaning takeover or hijacking.

It comes from the verb:

• 乗っ取る = to take over, to hijack

So:

• アカウントの乗っ取り = account takeover
• literally, the taking over of an account

Japanese often turns verb stems into nouns like this:

• 申し込み from 申し込む
• 立ち入り from 立ち入る
• 乗っ取り from 乗っ取る

The particle の links the two nouns.

• アカウント = account
• 乗っ取り = takeover
• アカウントの乗っ取り = account takeover

You can think of の here as meaning something like of or showing what is being affected:

• 会社の経営 = management of a company
• 個人情報の流出 = leak of personal information
• アカウントの乗っ取り = takeover of an account

Because 起こる is an intransitive verb, and the thing that occurs is marked with が.

• 事故が起こる = an accident happens
• 問題が起こる = a problem occurs
• 乗っ取りが起こる = a takeover occurs

So:

• アカウントの乗っ取りが起こりかねない
• An account takeover may occur / could easily occur

Using を with 起こる would be wrong, because 起こる is not transitive.

〜かねない means might well ..., could easily ..., or there is a real danger that ...

It is usually used for something bad or undesirable.

Examples:

• 事故が起こりかねない = an accident could easily happen
• 誤解されかねない = it could easily be misunderstood
• 情報が漏れかねない = the information might leak

So here:

• アカウントの乗っ取りが起こりかねない
• There is a real danger of account takeover
• Account takeover could easily occur

This is stronger and more cautionary than a plain かもしれない.

Both can mean might, but the nuance is different.

• かもしれない = simple possibility, neutral
• かねない = real possibility, often worrying or risky

Compare:

• 雨が降るかもしれない = It might rain.
• 事故が起こりかねない = An accident could easily happen / There is a danger of an accident.

So in warnings, manuals, and security messages, かねない is common because it sounds more serious.

Yes—normally, modern standard Japanese would write this as 起こりかねない.

The verb is:

• 起こる = to occur

Its stem is:

• 起こり

So the expected form is:

• アカウントの乗っ取りが起こりかねない

If you see 起り, it may be:

• a typo
• a stylistic/abbreviated spelling
• a result of inconsistent orthography

For learners, it is safest to use 起こりかねない.

Yes, the subject is omitted, which is very normal in Japanese.

The sentence does not explicitly say who ignores the suspicious login. Depending on context, it could mean:

• if you ignore suspicious logins
• if suspicious logins are ignored
• by ignoring suspicious logins

Japanese often leaves subjects unstated when they are obvious from context, especially in warnings, instructions, and notices.

It can suggest any of those, depending on context. In this sentence, the most natural interpretation is a cause/result relationship:

• If suspicious logins are ignored, account takeover may occur.

So although the form itself is just a connective 無視し, in context it implies something like:

• by ignoring
• when one ignores
• if one ignores

Japanese often leaves those logical links less explicit than English does.

It is understandable, but it sounds a little compressed and slightly awkward as written.

The biggest issue is 起り, which would normally be 起こり.

A more natural version would be:

• 不審なログインを無視すると、アカウントの乗っ取りが起こりかねない。

This version is clearer because 〜すると explicitly marks the condition:

• If you ignore suspicious logins, account takeover may occur.

But the original still feels like the kind of shortened warning you might see in technical or security-related writing.