Silveira was responding to numerous reports earlier Wednesday that hackers accessed close to 6.5 million hashed passwords from a LinkedIn database and posted it publicly on a Russian hacker forum. According to researchers who had seen the compromised data, more than 300,000 of the hashed passwords have already been decrypted and posted online in clear text.

LinkedIn had earlier said it was looking into those reports but had not confirmed the breach.

Tal Be'ery, security research leader at Imperva, claims to have seen the stolen data and said much more than 6.5 million passwords might have been compromised.

According to Be'ery, the passwords that have been posted online appear to be only those passwords that the hackers needed help in cracking. What the breached password list is missing are the usual easy-to-guess passwords that people commonly use to control access to online accounts, he said. The LinkedIn password file does not contain any of the common passwords that Imperva's researchers have typically run across when analyzing similar password breaches, he said.

"Most likely, the hacker has figured out the easy passwords and needs help with less common ones." So it's likely that only the more complicated passwords have been revealed so far, he theorized.