Credential theft
Infostealer vs Keylogger: What's the Difference?
A keylogger records what you type, staying on a device for weeks and capturing credentials as you enter them. An infostealer does the opposite — it runs once, copies everything already saved in the browser (passwords, session cookies, autofill data), and usually deletes itself within a minute. The practical difference is the response: resetting passwords handles a keylogger, but it does not handle an infostealer, because stolen session cookies stay valid until sessions are explicitly revoked
How a keylogger works
A keylogger installs and stays. It hooks into the operating system's input handling — or, in hardware versions, sits physically between the keyboard and the machine — and records what passes through.
The output is a stream of keystrokes, usually with context about which application was in focus. The attacker collects this periodically and reads through it looking for anything valuable.
Because it depends on you typing, coverage is limited by your behaviour. A password you haven't entered during the infection window is one it never sees. A password stored in a manager and autofilled is never typed at all, so it never appears in the log.
The trade-off from the attacker's side is time and exposure. Keeping software running on a device for weeks means more opportunities for endpoint protection to notice, and more chance the user spots something odd.
How an infostealer works
An infostealer doesn't wait for anything. It executes, and within seconds begins copying:
- Every credential saved in Chrome, Edge, Firefox and Brave
- The entire cookie store, including active session tokens
- Autofill data — addresses, phone numbers, sometimes card details
- Cryptocurrency wallet files and browser wallet extensions
- Documents matching certain patterns, often anything with "password" or "backup" in the filename
- A system profile: hostname, operating system, installed software, local IP, approximate location
- A screenshot of the desktop at that moment
Then it transmits the package and, in most cases, removes itself. Total runtime is frequently under a minute.
The complete output from one infection is a stealer log. It's a described machine, not just a list of passwords — a buyer can see whose it is, where they work, what's installed, and what was open at the time.
Side by side
How they work. A keylogger records keystrokes as they happen. An infostealer copies stored data in bulk.
How long they stay. A keylogger persists for weeks or months — it has to, since it depends on you typing. An infostealer runs for seconds to minutes and then exits.
What they capture. A keylogger gets only what you type while it's running. An infostealer gets everything already saved: credentials, session cookies, files, autofill data.
Session cookies. Keyloggers don't take them. Infostealers do, and this is the difference that matters most.
Context. Keyloggers rarely capture more than keystrokes. Infostealers usually include a desktop screenshot and a full system profile — hostname, installed software, location.
Detection. Keyloggers are easier to catch because they persist. Infostealers are harder, being brief and self-deleting.
Targeting. Keyloggers are usually aimed at a specific person. Infostealers are mass-distributed and opportunistic.
Volume. Keyloggers are uncommon. Infostealers are everywhere.
Why the distinction matters in practice
Detection windows differ enormously
A keylogger has to survive on the device to be useful, which gives behavioural detection weeks to notice it. An infostealer may exist on the machine for forty seconds. By the time anything analyses the behaviour, the process is gone and so is the file.
This is why infections are so often discovered externally — through credential exposure surfacing in monitoring data — rather than by the endpoint tooling that was running the whole time.
Scope differs enormously
A keylogger captures a password only if you typed it during the window it was active. An infostealer captures every credential the browser ever saved, regardless of when.
For most users that's the difference between a handful of accounts and every account they have ever logged into on that machine.
Response differs, and this is the one that catches people out
With a keylogger, resetting passwords is broadly sufficient. The attacker holds strings you typed; new strings render them useless.
With an infostealer, resetting passwords is not enough.
Stolen session cookies represent sessions that are already authenticated. An attacker can import a cookie into their own browser and be treated as the logged-in user — no password required, and no multi-factor prompt, because the MFA check was satisfied when the session was first created.
On most platforms, changing a password does not invalidate existing sessions. Which means the standard response — detect exposure, force a reset, consider it handled — leaves the attacker's access intact.
Sessions have to be revoked explicitly, and ideally before the password reset, so there is no window in which the attacker can observe the change and re-establish access.
Volume differs by orders of magnitude
Keyloggers are usually deliberate. Someone chose a target: a specific employee, a partner, a competitor.
Infostealers are commodity malware sold by subscription. The operator pays a monthly fee for a builder, a control panel and support, then distributes it as widely as possible through cracked software, malicious search advertising, fake CAPTCHA pages and social media links. They aren't targeting anyone — they're collecting from whoever runs the file.
The economics strongly favour the second model, which is why stealer logs exist in the millions and keylogger output does not.
Why your organization is exposed either way
The uncomfortable part of infostealer infections is that they usually don't happen on your equipment.
Someone installs a pirated application on a home laptop. That laptop has, at some point, been used to check work email, and the browser saved the password. The infection is personal; the exposure is corporate.
Your endpoint protection never saw it, because the device isn't yours. Your network logs show nothing, because nothing touched your network. The first signal available to you is the credential appearing for sale.
What to do about each
If you suspect a keylogger: isolate the device, run a full scan, change passwords from a different clean machine — not the infected one — and enable MFA everywhere.
If you suspect an infostealer: assume everything the browser stored is already gone.
- Revoke all active sessions for the affected accounts
- Reset the passwords
- Re-check MFA enrolments for devices you don't recognize
- Rotate API keys, tokens and SSH keys stored on that device
- Clean or isolate the source machine — otherwise the new credentials get harvested too
- Check whether the exposed password was reused elsewhere
Step 1 is the one most often skipped, and the one that matters most.
Common questions
Can antivirus detect both?
It detects known variants of both. Infostealer families are repacked continuously, sometimes daily, specifically to defeat signature matching, which makes detection inconsistent. Antivirus is worth running and shouldn't be relied on alone.
Does a password manager protect against either?
Against keyloggers, partially — autofill means the password is never typed. Against infostealers, only if the vault stays locked and the master password isn't saved in the browser.
Which is worse?
Infostealers, in most cases. They take more, they take it faster, and stolen session cookies bypass multi-factor authentication in a way keylogger output does not.
Can one piece of malware do both?
Yes. Some families include keylogging alongside bulk collection, and some intrusions deploy a keylogger after an infostealer has provided the initial foothold.
How would I know which one hit me?
Often you wouldn't, from the inside. The practical approach is to assume the worse case and treat stored credentials and sessions as compromised.
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