Laid off -- tell employers?

I was recently part of the big round of layoffs across IB and have received conflicting advice. I know it's easier to get a job while you're already employed, but some people claim that employers will do thorough background checks. Would you (1) not disclose that you were laid off unless directly asked during an interview; (2) disclose your termination date on your resume but not address it in your cover letter; or (3) disclose termination date on resume and also explain it on your cover letter?

The cover letter explanation would be one sentence explaining that it was part of firmwide layoffs due to widely publicized deal slow down.