VirusTotal

What it does

Scans files and URLs against 70+ antivirus engines and URL/domain blacklisting services. Provides community comments and behavioral analysis. API available for automation.

When to use it

• Checking if file is known malware
• URL reputation checks
• Getting multiple AV opinions

When not to use it

• Code deobfuscation
• Understanding what code does
• When you need to read the source

Limitations

• Only detects known threats
• Uploads are shared with AV vendors
• Rate limited without API key