Infostealer Malware: How It Steals Passwords and Cookies and How to Stay Safe

Infostealer Malware: How Hackers Steal Passwords and Cookies (And How to Stop It)

What Is Infostealer Malware?

An infostealer is a type of malware designed to collect sensitive information from an infected device and send that information to an attacker. This is different from ransomware, which typically encrypts or locks files and demands payment. Infostealers often try to operate quietly so they can collect information before the victim realizes the device has been compromised.

When the infostealer sends the information to the attacker it usually gets. Traded on secret websites in packages called logs. Each log can have all the information taken from one computer, which is often enough for a bad person to get into someones email, cloud storage, banking apps or crypto wallet without having to guess the password.

Security researchers have noticed infostealer attacks in recent years. One reason is that stealing data can be very profitable. Another reason is that many people still use the password, for multiple websites making it easier for hackers to access more accounts.

What Infostealers Actually Target

Understanding what these programs go after helps explain why they are so damaging, even though they do not "hack" anything in the traditional sense.

Saved Browser Passwords

Most browsers can save passwords to make sign-ins easier. Those credentials are stored in protected browser or operating-system storage, but malware specifically designed to steal information may attempt to access browser credential stores. The exact protection and attack method can vary by browser, operating system and malware family.

Session Cookies

When you sign in to a website, your browser may receive a session cookie that helps the site remember your authenticated session. Some infostealers are capable of stealing browser cookies or session tokens. If an attacker obtains a valid session token, they may be able to access an account without entering the password again. In some cases, a stolen session can also reduce the protection provided by additional authentication because the attacker is abusing an already authenticated session.

This is why session-cookie theft is a serious security concern. The attacker does not necessarily need to know the account password if a valid authenticated session can be abused. Session cookies are separate from saved browser passwords and are used by websites to maintain an authenticated session.

Autofill Data and Saved Payment Details

browsers save information like your name, address and sometimes part of your card details. This makes it easier to checkout.. Infostealers can get this information too. They can use it to pretend to be you even if they do not have your card number. This is a problem because it can lead to identity fraud. Infostealers can get a head start on this fraud because they have some of your information already.

Cryptocurrency Wallets

If you use a cryptocurrency wallet in your browser infostealers will look for your wallet files and seed phrases on your device. They want to steal your cryptocurrency. This is a problem when you get an infostealer infection. Once someone steals your cryptocurrency you usually cannot get it back. This is because cryptocurrency transactions cannot be reversed.

Messaging App Data

Some infostealers also look at data from apps like Telegram or Discord on your device. They want to get information, from these apps because they can use it to scam you. Infostealers can use your Telegram or Discord account to trick you or your friends into doing something you should not do. This is why it is a problem when infostealers get into your messaging apps. Infostealers and cryptocurrency wallets are a combination. Infostealers can steal your cryptocurrency. Use your messaging apps to scam you.

How Infostealers Usually Get Onto a Device

Infostealers commonly reach devices through social engineering and deceptive downloads. Understanding the common delivery methods makes it easier to recognize suspicious files, websites and messages before they lead to an infection.

Some things can give you infostealers like:

• Cracked software
• Game cheats

When you download cracked software or game cheats you are taking a risk. These things often come with infostealers. People are not careful when they download these things because they think they are getting something for free.. That is exactly what the bad people are counting on.

You can also get infostealers from phishing emails. These emails have attachments or links that look safe. They might look like an invoice or a job offer. The bad people want you to click on the link or open the attachment without thinking.

Sometimes you can get infostealers from ads or fake download sites. When you search for software you might find a fake website that looks like the real thing.. When you download the software you get a trojan instead.

Malicious or compromised browser extensions can also create security risks. An extension with excessive or abusive permissions may be able to access sensitive browser data, so install extensions carefully and remove those you no longer trust or use.

You have to be careful when you are looking for a job. Some job offers are fake. The bad people might say they are recruiters and ask you to download a test or a tool.. It is really an infostealer. This happens on platforms, like LinkedIn and Discord. The bad people use these platforms to trick people into downloading infostealers. Infostealers are a problem and you have to be careful to avoid them. Infostealers can hurt you if you are not careful.

The common thread across all of these is that the malware relies on the user taking an action, such as downloading a file or enabling a browser add-on. That is also why awareness is such an effective defense.

Warning Signs You Might Be Infected

Infostealers are sneaky so you might not even notice they are there. There are some things you should look out for.

Here are a few signs that something is going on with your computer or accounts:

• Your accounts show unfamiliar login activity or sessions you do not recognize.
• Friends receive messages from your social media or messaging accounts that you did not send.
• You find browser extensions that you do not remember installing.
• Your antivirus or security software detects suspicious or unwanted software.
• You notice unusual activity on important accounts after downloading suspicious software or files.
• Your accounts show other unexpected security changes or access attempts.

If you see one of these things it does not mean you have an infostealer..If you notice a few of these things happening at the same time you should really look into it and find out what is going on with your infostealers and your computer.

How to Protect Yourself From Infostealers

You do not need to be a cybersecurity expert to significantly lower your risk. Most of the effective steps are simple habits.

Use a reputable password manager and avoid relying unnecessarily on browser-stored passwords.

A reputable password manager can help you create and manage unique passwords. However, a password manager is not a complete defense against malware on a compromised device, so it should be combined with other security measures such as software updates, multifactor authentication and safe downloading habits.

Turn on multifactor authentication (MFA) for important accounts. When available, consider using a passkey or an authenticator app.

MFA provides an additional layer of protection if a password is stolen. Passkeys can provide strong phishing resistance, while authenticator apps are generally preferable to SMS when stronger options are available. However, MFA does not guarantee protection if an attacker obtains an already authenticated session or other authentication tokens.

Do not use pirated software, cracked games and so called versions of paid tools.

They are not really free. If a program is something you normally have to pay for and you find a cracked copy that is a major red flag, not a good deal.

Treat pirated software. Cracked games as a big warning sign. Remember, pirated software and cracked games are not safe to use. So always be careful, with pirated software. Cracked games.

Only install browser extensions from official stores, and review them occasionally.  

Remove anything you do not actively use or do not remember installing.

Keep your operating system and browser updated.  

Updates frequently patch the exact vulnerabilities that malware relies on to install itself quietly.

Use reputable antivirus or endpoint protection software  

and let it run scheduled scans instead of only reacting to alerts.

Be cautious with email attachments and unexpected links,  

especially ones tied to invoices, job offers, or "urgent" account issues. Verify the sender through a separate channel if anything feels off.

Log out of accounts and clear sessions on shared or public computers.  

Session cookies left active on a device you no longer control are a real risk.

Regularly review which devices and sessions are logged into your important accounts.  

Most email providers, banks, and social platforms show this in their security settings, and you can remotely sign out of anything unfamiliar.

What to Do If You Think You Are Infected

If you suspect an infostealer has been running on your device, speed matters more than anything else.

• Disconnect the suspected device from the internet to limit further communication with the malware.
• Run a scan using reputable antivirus or anti-malware software.
• From a device you trust, change passwords for important accounts, starting with email, banking and other financial accounts.
• Enable multifactor authentication where available.
• Sign out of active sessions and revoke suspicious sessions or tokens where the service provides that option.
• Review financial accounts and cryptocurrency wallets for unauthorized activity.
• If you cannot confirm that the malware has been completely removed, consider resetting the device or reinstalling the operating system.

If sensitive financial or identity information was involved, it is also worth reporting the incident to your bank and, depending on your country, a relevant cybercrime reporting authority.

Why Stolen Data Can Stay Dangerous for Months

The effects of an infostealer infection can continue after the malware is removed because stolen credentials, cookies or other information may already have been collected. Attackers may use or sell stolen data later, meaning a compromised device can create account-security risks even after the original infection is no longer active. If a device was infected, accounts used on that device during the affected period should be reviewed rather than focusing only on the first account that showed suspicious activity.

This is also why the people, in charge of security keep telling us to log out of everything and reset our passwords even after it seems like the problem is fixed. Just because you cleaned your device does not mean that the old passwords and cookies are not already being sold to people. Infostealer damage can still cause problems even after you think you have fixed everything.

Common Questions About Infostealer Malware

Does antivirus software fully protect against infostealers? 

Reputable antivirus software blocks a large share of known infostealer variants, but new versions appear constantly, and some are specifically designed to slip past detection for a short window. Antivirus should be one layer of protection, not the only one you rely on.

Can an infostealer infect a phone. Is it only a problem for computers?

Infostealers usually target Windows computers. There are also types of infostealers that target mobile phones. These mobile infostealers often come from apps that you can download from places other than official app stores. Sometimes they come from links that people send you through messaging apps. If you only download apps from app stores you are much safer, from infostealers.

If I do not save passwords in my browser, am I safe?

Not saving passwords in a browser can reduce one source of credential exposure, but it does not eliminate the risk. Depending on the malware and device, infostealers may also target session cookies, authentication tokens, autofill information or other sensitive data. Browser password storage is only one part of the overall risk.

Is it enough to just change my password after an infection?

No. Because infostealers often steal session cookies along with passwords changing the password by itself might not stop an attacker if the old session is still active. It’s important to sign out of all sessions and set up two-factor authentication. This is just as important, as updating the password.

Final Thoughts

The Infostealer malware is successful because it targets the convenience features that people already trust, like saved passwords and autofill data and stay logged in sessions. This Infostealer malware does not need to guess anything if your browser's already willing to give the information away.

The good news is that defending against Infostealer malware is not complicated. You can use a password manager and enable strong two-factor authentication. You should also avoid downloading pirated software and stay alert to phishing attempts.

These steps can significantly reduce your risk, but no security measure can guarantee that an infostealer infection will never occur. Be cautious with unfamiliar downloads, browser extensions and offers of free software that seem too good to be true. If something asks you to install unexpected software or provide sensitive information, verify it before continuing.