Microsoft said a Russian-linked hacking group attacked its corporate systems, getting into a "small number” of email accounts, including those of senior leadership and employees who work in cybersecurity and legal.

The company said it’s acting immediately to fix older systems, which will probably cause some disruption.

The hacking group doesn’t appear to have accessed customers’ systems or Microsoft servers that run outward-facing products, the software giant said Friday in a blog post. Microsoft also has no evidence the group, named Midnight Blizzard, got into source code or artificial intelligence systems.