LLM Security Checklist for Enterprises in 2026

Frequently Asked Questions

01.What should an enterprise LLM security checklist cover in 2026?

In my view, eight records: a data exposure map, an untrusted-input register, a tool permission register, a provenance record for models and data, your own interaction log, signed vendor terms, an incident runbook and a note on your AI Act role. Each one should pass or fail, not describe an intention.

02.Can prompt injection be fully prevented?

Not reliably today. Anthropic reports that a one percent attack success rate for Claude Opus 4.5 in browser use still represents meaningful risk, and that no browser agent is immune to prompt injection (Anthropic, November 2025). That is why I limit what an agent can do, with least-privilege tools and human approval for high-risk actions.

03.Does the EU AI Act require LLM security controls in 2026?

For most companies building on a model API, not directly yet. The Article 15 cybersecurity duty applies to Annex III high-risk systems from 2 December 2027 under Regulation (EU) 2026/1744 (EUR-Lex, July 2026), and Article 55 binds providers of general-purpose AI models with systemic risk. GDPR security and breach duties already apply.

04.How fast must a company report an LLM data leak under GDPR?

As controller: without undue delay and, where feasible, within 72 hours of becoming aware of a personal data breach, unless it is unlikely to result in a risk to people (GDPR Article 33, April 2016). Details may follow in phases, but the team still needs logs showing what the model and its tools touched.