threats to the service. Days later, Valve reported that the hack had compromised one of its customer databases, potentially allowing the perpetrators to access customer information; including encrypted password and credit card details. At that time, Valve was not aware whether the intruders actually accessed this information or discovered the encryption method, but nevertheless warned users to be alert for fraudulent activity. Valve added Steam Guard functionality to the Steam client in March 2011 to protect against the hijacking of accounts via phishing schemes, one of the largest support problems Valve had at the time. Steam Guard was advertised to take advantage of the identity protection provided by Intel's second-generation Core processors and compatible motherboard hardware, which allows users to lock their account to a specific computer. Once locked, activity by that account on other computers must first be approved by the user on the locked computer. Support APIs for Steam Guard are available to third-party developers through Steamworks. Steam Guard also offers two-factor, risk-based authentication that uses a one-time verification code sent to a verified email address associated with the Steam account; this was later expanded to include two-factor authentication through the Steam mobile application, known as Steam Guard Mobile Authenticator. If Steam Guard is enabled, the verification code is sent each time the account is used from an unknown machine. In 2015, between Steam-based game inventories, trading cards, and other virtual goods attached to a user's account, Valve stated that the potential monetary value had drawn hackers to try to access user accounts for financial benefit, and continue to encourage users to secure accounts with Steam Guard, when trading was introduced in 2011. Valve reported that in December 2015, around 77,000 accounts per month were hijacked, enabling the hijackers to empty out the user's inventory of items through the trading features. To improve security, the company announced that new restrictions would be added in March 2016, under which 15-day holds are placed on traded items unless they activate, and authenticate with Steam Guard Mobile Authenticator. After a Counter-Strike: Global Offensive gambling controversy, Valve stated it is cracking down on third-party websites using Steam inventory trading for Skin gambling in July 2016. ReVuln, a commercial vulnerability research firm, published a paper in October 2012 that said the Steam browser protocol was posing a security risk by enabling malicious exploits through a simple user click on a maliciously crafted steam://