Korisnički podaci su zaštićeni pristupnom lozinkom.

Podaci is the plural of podatak, which means data item / piece of information.

A useful thing to know is that Serbian often treats podaci as a normal plural count noun, whereas English often uses data as a mass noun or collective noun.

• podatak = a piece of data
• podaci = data

In this sentence, podaci is the subject, so it is in the nominative plural.

Korisnički is an adjective meaning user-related / belonging to the user / user-.

So:

• korisnik = user
• korisnički = user, user-related

Serbian often uses adjectives where English uses a noun modifier. English says user data; Serbian naturally says korisnički podaci.

The form korisnika podaci would not be the normal way to express this idea here.

It is an adjective, and it agrees with podaci.

Because podaci is:

• masculine
• plural
• nominative

the adjective also appears in the matching form:

• korisnički

This is one of the core features of Serbian: adjectives agree with the nouns they describe in gender, number, and case.

Su is the 3rd person plural present form of biti (to be).

So here:

• podaci = the data
• su zaštićeni = are protected

This is completely normal Serbian structure. The sentence is built like:

• Subject + to be + adjective/passive participle

So su is needed because the subject is plural.

Compare:

• Podatak je zaštićen. = The data item is protected.
• Podaci su zaštićeni. = The data are protected.

Because zaštićeni agrees with podaci.

It is a passive-participle-like adjective meaning protected, and it must match the noun it refers to.

Since podaci is:

• masculine
• plural
• nominative

the correct form is:

• zaštićeni

Compare:

• Podatak je zaštićen. = singular masculine
• Podaci su zaštićeni. = plural masculine
• Lozinka je zaštićena. = singular feminine

So the ending changes according to agreement.

In this sentence, it functions as part of a passive-like construction: are protected.

Serbian often expresses this with:

• biti
  • passive participle / adjectival form

So su zaštićeni corresponds closely to English are protected.

At the same time, this form behaves like an adjective because it agrees with the noun in gender, number, and case.

So the short answer is: it is grammatically adjective-like, but semantically it gives a passive meaning.

Because after zaštićeni here, Serbian uses the instrumental case to express the means or instrument by which something is protected.

So:

• pristupna lozinka = an access password (nominative)
• pristupnom lozinkom = with an access password / by an access password (instrumental)

This is one of the most important things to notice in the sentence.

The instrumental here answers the idea:

• Protected by what?
• With what means?

Answer:

• pristupnom lozinkom

It is in the instrumental singular.

Both words change because:

• pristupnom is an adjective
• lozinkom is the noun

In Serbian, adjectives agree with the nouns they modify in gender, number, and case.

Base form:

• pristupna lozinka

Instrumental singular:

• pristupnom lozinkom

Because lozinka is:

• feminine
• singular
• instrumental

the adjective must match it:

• pristupnom

Literally, pristupna lozinka is something like access password.

• pristup = access
• lozinka = password

In natural English, you would often simply say password, but Serbian may specify pristupna lozinka to make it clear that this is the password used to gain access.

So yes, it is basically password, but with a slightly more explicit sense of access password.

Yes. Serbian word order is more flexible than English.

The neutral order here is:

• Korisnički podaci su zaštićeni pristupnom lozinkom.

But other orders are possible depending on emphasis, for example:

• Korisnički podaci pristupnom lozinkom su zaštićeni.
• Pristupnom lozinkom su zaštićeni korisnički podaci.

The original version sounds natural and neutral. Other versions may sound more marked or may emphasize how the data are protected.

Because Serbian has no articles.

English distinguishes:

• a password
• the password

Serbian does not do this with separate words. The meaning is understood from context.

So pristupnom lozinkom could be understood as:

• with an access password
• with the access password

depending on the situation.

The same applies to korisnički podaci:

• user data
• the user data

Context tells you which is intended.

The singular would be:

Korisnički podatak je zaštićen pristupnom lozinkom.

Changes:

• podaci → podatak
• su → je
• zaštićeni → zaštićen

This is a good way to see how agreement works in Serbian.

Plural:

• Korisnički podaci su zaštićeni pristupnom lozinkom.

Singular:

• Korisnički podatak je zaštićen pristupnom lozinkom.

Yes. Lozinka is the normal everyday Serbian word for password.

Learners sometimes also encounter šifra, which can mean code, PIN, password, or passcode depending on context. But lozinka is the clearest and most standard word for an actual password, especially in formal or technical language.

So in this sentence, lozinka is exactly what you would expect.