British Airways' air-miles accounts, the coding site GitHub and the work chat service Slack have all been hit in the latest wave of cyber-attacks.
The firms have all notified their users of the incidents, which varied in approach and do not appear to be connected.
In addition, several Uber users have complained of their accounts being hacked. However, the car pick-up service said it had “found no evidence of a breach”.
The firms have dealt with the attacks in different ways, and BA has been criticised for how it responded. Complaints about points being stolen from the BA’s Executive Club scheme date back at least a fortnight.
One user said their account had been used by someone else to book a hotel room in Spain, while others reported that their list of transactions showed “ex-gratia” deductions that had wiped out their entire credit.
“I checked my account yesterday and found that the mobile number had been changed to a Russian one. I changed it back and my miles are still there. Passwords now changed,” reported another member, who appeared to have had a narrow escape.
A spokesman for BA said that it believed only “a small number” of its frequent flyers were affected.
“This appears to have been the result of a third party using information obtained elsewhere on the internet, via an automated process, to try to gain access to some accounts,” he said.
“We would like to reassure customers that, at this stage, we are not aware of any access to any subsequent information pages within accounts, including travel histories or payment card details.”