Over the last nine days, the the Office of Personnel Management has sent e-mail notices to hundreds of thousands of federal employees to notify them of the breach and recommend that they click on a link to a private contractor’s Web site to sign up for credit monitoring and other protections.

But those e-mails have been met with increasing alarm by employees — along with retirees and former employees with personal data at risk — who worry that the communications may be a form of “spear phishing” used by adversaries to penetrate sensitive government computer systems.

After the Defense Department raised a red flag about the e-mails its 750,000 civilian employees were starting to receive, OPM officials said late Wednesday that the government had suspended its electronic notifications this week.