Tens of thousands of new digital certificates have been issued by Comodo in the wake of the “Heartbleed” security flaw, which has put Internet users’ data at risk.

One of New Jersey-based Comodo’s main business lines is issuing the digital certificates that encrypt traffic between users and a Web service, a critical shield that protects users from spying by third parties.

Over the last day or so, Comodo has seen a huge uptick in requests for new digital certificates from website operators, said Robin Alden, Comodo’s chief technology officer.

“The last couple of days, we’ve seen replacement rates running at somewhere between 10 to 12 times the normal rate than were replacing a week ago,” Alden said. “That’s obviously fallout from this.”

The spike comes after the disclosure on Monday of the so-called Heartbleed vulnerability in an open-source software package, OpenSSL, widely used in operating systems, routers and networking equipment.

It is believed the flaw might in some cases allow an attacker to obtain the private key for a SSL (Secure Sockets Layer) certificate. With that private key, an attacker could create a fake website with an SSL certificate that passes the verification test indicated by a browser’s padlock.

The flaw can also be used by an attacker to pull sensitive data in 64K chunks from a Web server, including login information from users who recently used the service.

Comodo's Robin Alden.

Netcraft, a UK-based company that specializes in security and compiles statistics on Web servers, wrote on Tuesday that the OpenSSL vulnerability affects as many as 500,000 websites using digital certificates issued by trusted certificate authorities.

On Thursday, the Federal Financial Institutions Examination Council warned that financial institutions should consider replacing their digital certificates after patching the Heartbleed bug.

It was unknown if cybercriminals or state-sponsored hackers had been exploiting the flaw prior to its public release on Monday since the attacks are thought to not leave traces in server logs.

Comodo, which is the second-largest issuer of SSL certificates behind Symantec’s VeriSign division, has been contacting customers and conducting automated scanning of websites using its certificates to try to find vulnerable ones, Alden said.

“We’re going to keep looking for affected servers and detect whether the server is capable of being exploited,” Alden said.

About 70 percent of Comodo’s customers who have replaced their digital certificate have revoked the old one, Alden said. Certificates that are no longer valid are blacklisted, and browsers that come across a website using one will typically display a warning.

The next step for affected websites that were vulnerable is issuing a password reset to users, as the passwords could have been compromised, Alden said. But the vast scope of the problem due to the wide use of OpenSSL means the remediation process could be lengthy.

“It’s quite early in the life of this incident,” Alden said. “There’s going to be more fallout from this thing to come. In time, I think a lot of users are going to have to change their passwords.”