fell for a tech support scam, had someone remotely access his laptop. How much damage could be done?
Tons. My mom also fell for that sh*t. She ought know better but … well, … sh*t happens.
likely is it that any files or personal information were taken?
Or that some type of persistent back-door was installed, etc.
I might suggest, if you want to figure out (gu)estimated probabilities, if you / your friend has information on these particular scammers - do some research, see what they typically do. They’re all scum, but the danger level varies. E.g. many mostly just go in, show on screen stuff user doesn’t understand, and convince 'em they need to spend more money on their services - and get card (or account) data and charge for that … and might not be much worse, 'cause they want the repeat business of hitting the same “customers” with same/similar scams repeatedly. Others are much nastier, e.g. grabbing sensitive documents, maybe keytroke loggers, etc., might install a backdoor or quite stealth backdoor. And also, depending what remote access software was used, your friend may or may not have seen all that they were doing.
Tons. My mom also fell for that sh*t. She ought know better but … well, … sh*t happens.
Or that some type of persistent back-door was installed, etc.
I might suggest, if you want to figure out (gu)estimated probabilities, if you / your friend has information on these particular scammers - do some research, see what they typically do. They’re all scum, but the danger level varies. E.g. many mostly just go in, show on screen stuff user doesn’t understand, and convince 'em they need to spend more money on their services - and get card (or account) data and charge for that … and might not be much worse, 'cause they want the repeat business of hitting the same “customers” with same/similar scams repeatedly. Others are much nastier, e.g. grabbing sensitive documents, maybe keytroke loggers, etc., might install a backdoor or quite stealth backdoor. And also, depending what remote access software was used, your friend may or may not have seen all that they were doing.