Twitter said Monday that hackers broke into an unspecified number of accounts and sent spam promoting acai berry drinks. Twitter says the passwords came from an earlier breach at Gawker Media, which runs Gawker, Gizmodo and other technology and media sites. People who used the same passwords for both sites were vulnerable.

Twitter says it doesn’t know how many of its 175 million users were affected. It says it proactively reset passwords it suspects were compromised. Twitter says only a small number of accounts were affected.

Attacks on social networking sites such as Twitter and Facebook are popular because people are more inclined to click on links appearing from friends, rather than e-mail spam.