Shares of single sign-on giant Citrix tumbled Friday on news the FBI is investigating a cyber-intrusion.

The 2 percent dip pushes Citrix into the red for the year to date. The stock is up 6 percent for the last 12 months and trades roughly 15 percent off 52-week highs.

The company said in a blog post that the FBI contacted the company March 6 to report an intrusion by cybercriminals to the Citrix network.

"While our investigation is ongoing, based on what we know to date, it appears that the hackers may have accessed and downloaded business documents. The specific documents that may have been accessed, however, are currently unknown. At this time, there is no indication that the security of any Citrix product or service was compromised," the company said.

A breach of Citrix's networks could potentially have significant reach. Citrix provides virtual private network, or VPN, access and credentials to 400,000 companies and other organizations worldwide, including 98 percent of the Fortune 500, according to the company.

In its statement, the company said business documents had been downloaded and stolen as part of the attack, which was executed by exploiting weak passwords. Citrix said it does not yet know the nature of the business documents.

The company said it is "moving as quickly as possible, with the understanding that these investigations are complex, dynamic and require time to conduct properly." Citrix said it has taken action to contain the incident.