Thanks Tech & David for replies. David, I’m not asking about those “security alert” email/fake bank website type info-stealing scams, where the victim is fooled into giving away their idetails, but instead about bits of nasty code picked up in emails, by clicking onto thingies in a website, or sneaking in with free software.
In the report I mentioned (in New Scientist) the thefts were apparently accomplished by malware embedded in a free anti-spam filter (not very free, as it turned out).