Steam's Summer Sale kicked off on Thursday amidst a "test" denial of service attack by CyberTeam. Two products that have received discounts are the Steam Controller (70% off) and Steam Link (30% off).
Some users are unable to properly access Steam servers during the the 2017 Summer Sale. Hacker group CyberTeam claimed responsibility and promised a full attack targeting all servers is on the way.
A hacking group, going by the name of CyberTeam, was responsible for Skype's downtime since Monday. The attack appears to be winding down but now they're getting ready to hit Steam with a DDoS attack.