The server contained the stolen names, addresses, phone numbers and e-mail addresses of people who used Monster's service. The company was still determining the number of people affected by the breach on Wednesday. It did not disclose the location of the server.

The Monster incident is one of a growing number of prominent data breaches highlighting continuing difficulties with Internet security.

Hackers obtained the log-in credentials for companies seeking employees and used the credentials to access Monster.com's database of job seekers. An automated Trojan, dubbed Infostealer.Monstres by security vendor Symantec, then transmitted the personal information to the rogue server.

Symantec said earlier in the week it had found a server containing 1.6 million records belonging to hundreds of thousands of Monster users, mostly in the United States. It was unclear Thursday morning if the server Monster shut down is the same one that Symantec found. A Monster spokeswoman contacted in London could not provide more information.

As part of a multistep attack, the job seekers were then sent e-mails with links to at least two kinds of malicious software. One tries to collect log-in details for financial sites, and the other is designed to encrypt data on a PC, asking for a ransom to decode the data.

Monster said it will contact the people believed to have been affected by the attacks. It also posted an example of what a phishing e-mail looks like on its website.

"Regrettably, opportunistic criminals are increasingly using the Internet for illegitimate purposes," the company said in a statement.