Monster.com revealed in an online notice that hackers had gained access to its database of user IDs, passwords, names, e-mail addresses and phone numbers. Information from users' CVs was not touched, it said.
To date, the company's investigations have not identified any attempts to use the personal data, but it warned users about the dangers of phishing e-mails and said they should change their passwords as soon as possible.
The latest hack looks like a common trick favored by household burglars to return to the scene of their previous crimes. The breach came just days after Monster.com had unveiled a new Web site boasting better security features and a collection of job hunting tools. In August 2007 hackers made off with thousands of e-mail addresses used to propagate a virus that encrypted people's files.
To add to the damaging effects of the latest intrusion, Monster.com is the engine that drives the US government's main recruitment site.