TripAdvisor's email list compromised
tripadvisor.com
tripadvisor.com
It doesn't talk about the exploited service, the vulnerability, if it was known, etc.
Instead they tell us 'signs of spam'.
That being said, "It affected a portion of our membership" is the least useful answer to "How many members were impacted?" that I have ever seen.
Is a pretty clear assertion that they are aware of how the attack took place and know how to patch the issue.
Hopefully once damage control is complete, we'll learn more.
The temptation will often to be hide this kind of thing, claiming it's irrelevant (which typically just means it's embarrassing).
Also, I'm glad to see this isn't another incident where a vulnerability reveals a site is storing passwords in plaintext (like Gizmodo). Seriously, why do people do this?
Maybe they think it's an acronym?