Adware is malware that displays ads, and closely related to that is malware that uses your computer to silently click on ads. Both are relatively harmless for the infected system, but sometimes adware is used to download more damaging malware. Moreover, the fact that adware was installed in the first place, suggests a mistake was made somewhere.

Some malware is used to engage in behaviour targeting other systems, by taking part in DDoS attacks, sending spam, or acting as proxies. The main risk for infected systems here is the use of resources, which can be costly, and the risk of the IP address ending up on blocklists.

Finally, scareware is malware that pretends to be harmful but only scares the user. For example, scareware may claim to be ransomware and demand a ransom, or claim to be a warning from the police that requires a fine to be paid.