Spimming is defined in digital forensics and cybercrime references as spam over instant messaging (IM). It is a social-engineering variant where attackers use instant messaging platforms (and sometimes chat apps) to deliver unsolicited bulk messages containing malicious links, fraudulent offers, credential-harvesting lures, or malware downloads. Because IM messages are often delivered in real time and can appear to come from known contacts (via compromised accounts), spimming can achieve higher click-through rates than traditional email spam. For investigators, spimming incidents commonly leave artifacts such as chat logs, message timestamps, sender identifiers, embedded URLs, and sometimes downloaded payload traces on the endpoint. These artifacts help establish attacker infrastructure (domains, IPs), victim interaction (click events, file creation), and timeline correlation with network logs.

The other options do not match the ''IM as a tool to spread spam'' description. Whaling targets high-profile individuals via highly tailored phishing, typically email-based. Pharming redirects users to fraudulent websites (often via DNS or host-file manipulation) without relying on bulk IM spam. Spear phishing is targeted phishing toward specific individuals or groups, not necessarily IM spam. Therefore, the phishing/spam attack that exploits instant messaging platforms is Spimming (C).