The hacking group LAPSUS$ claims to have accessed internal Microsoft systems and stolen 37 GB of source code, including code from Bing, Cortana, and more.

“We are aware of the claims and are investigating,” a terse Microsoft statement notes of the hack.

The group posted a screenshot to its Telegram channel on Sunday morning—an edited version of which can be seen above—to prove that it had obtained access to Microsoft’s internal systems. Then, on Monday, it posted 9 GB of archives files containing over 250 Microsoft source code projects to a torrent site. LAPSUS$ claims the source code dump represents 90 percent of the source code for Bing and about 45 percent of the code for Bing Maps and Cortana. The uncompressed archives are about 37 GB in size.

Security researchers who have viewed the source code say it appears legitimate. Not helping matters, LAPSUS$ has previously successfully hacked NVIDIA, Samsung, Vodafone, Ubisoft, and Mercado Libre.