A system failure hitting The Royal Bank of Scotland (RBS) on Cyber Monday kept more than 1 million UK customers from making online purchases, withdrawing money from ATM machines or carrying out other transactions via online and mobile banking.

On Tuesday, Ross McEwan, CEO of RBS, told Reuters that “for decades, RBS failed to invest properly in its systems” – a misstep that led to the bank's “unacceptable” systems failure for hours on Monday, easily one of the biggest online shopping days each year for consumers.

The glitch also impacted Ulster Bank and NatWest, which are a part of The Royal Bank of Scotland Group.

On Tuesday, when RBS Group posted a notice on its site about the outage, numerous customers commented that issues still plagued their accounts.