Make sure the files you download from the web aren't malicious! Metascan Online for Chrome, by OPSWAT, allows you to scan all downloads, or specific files, for malware using 40+ commercial anti-malware engines. Using many anti-malware engines helps ensure that more viruses, spyware, Trojan and other threats can be detected - malware that might be missed by a single anti-malware engine.
Limitations: This extension gives you the ability to scan downloads (up to 80 MB). You will need to set up a free account to receive your free API key which will let you check scan results for up to 1000 previously seen files per hour and scan up to 25 new or unknown files per hour.