Infostealers have become one of the most prolific and damaging categories of malware, and the log is the currency they produce. An infostealer infects a victim device — often through a pirated-software download, a malicious attachment, a browser extension, or a drive-by download — and then harvests everything useful it can find: saved passwords from browsers, autofill data, session cookies, cryptocurrency wallets, SSH keys, FTP credentials, and files matching patterns of interest. The harvested data is packaged into a log and exfiltrated.
What makes infostealer logs particularly dangerous is the session cookie. Multi-factor authentication, properly enforced, defeats most credential theft: a stolen password alone is not enough to log in. But a stolen session cookie can often be replayed to bypass authentication entirely, because it represents an already-authenticated session. This is how attackers turn an infostealer infection on a personal laptop into access to a corporate VPN, email, or cloud console — the victim authenticated at home, the cookie was stolen, and the attacker steps into the session without ever seeing a login prompt.
The stolen logs are monetised in several ways. They are sold on criminal marketplaces to other actors, used directly by the crew that stole them to conduct account takeover, or aggregated into enormous databases that are queried by other criminals. The scale is significant: billions of records have been collected from infostealer infections, and the major dark-web intelligence platforms index tens of billions of records across credential and cookie leaks. An organisation's exposure is almost always larger than its security team realises.
Detection of infostealer exposure is therefore a high-value defensive activity. By monitoring for the organisation's domains, email addresses, and known cookies in infostealer-log datasets, a security team can identify devices that were compromised — sometimes months earlier — and force password resets, invalidate sessions, and investigate what was accessed. This is one of the most concrete and actionable outputs of dark-web monitoring, and it directly prevents the account takeovers that lead to breaches. Critically, the affected device is often a personal device that never touched the corporate network, which means conventional EDR would never see it.
Passeca delivers infostealer-log monitoring through Signals, which continuously surveils darknet markets, paste sites, and forums for an organisation's exposed credentials and cookies, with over forty billion indexed records and alerts by email, Slack, and Telegram, plus SIEM and SOAR export from the Professional plan. The free exposure check shows an organisation whether its domains appear in current infostealer datasets, and the full service provides ongoing alerting so that a stolen credential is detected and revoked before it can be used.