Citrix found out from the FBI on March 6, 2019, about a security breach into its internal network which led to the cybercriminals behind the attack being able to access and steal a set of business documents. No Citrix products or services were impacted by the attack. The FBI has advised that the hackers likely used a tactic known as password spraying, a technique that exploits weak passwords. NBC News reports that Iranian-backed hackers were behind this breach and that they managed to steal between 6-10 TB of documents.
Source: https://www.bleepingcomputer.com/news/security/citrix-learns-about-internal-network-security-breach-from-fbi/