Oh my gosh. That sickens me we have humans on this planet that do this to people! I recently had a phone call telling me that since I was such a good citizen I won $9,000 per a Grant from the government. I only needed to call another number and give them "my information". It's sad too that someone lowers themselves to this kind of crime.
Well, I also was infected by a so called virus and a Microsoft "official" told me I needed to buy a special cleaner. They just had me look at the event errors and it was supposed to frighten me.
First things first. If he got into your computer they want financial and Identity information. I doubt they actually put a virus on the computer since they got in the old fashioned way. Trust of someone helping. This burns me up. So check her credit cards and bank accounts and all of that and notify officials as soon as you can.
Check with social security to be sure they aren't diverting her direct deposit. There is an online site called my social security that is helpful with that. Or, just call social security immediately. They can put a hold or pause on anyone making changes with he payments.
What else? Hm. Those are the two biggies. Call the credit card people/bank/ social security and also any online groups she may not want another person accessing. Change all of her user ID's and passwords. It's a big hassle but if they find any sort of path to money or property or online purchases, of course you need to nip that in the bud right now. Tell your mom she's OK and shes not the first one scammed by these predictors with no soul. Good luck. I'd change her phone numbers too and email.
As for a virus. Malware-bytes is best. But I would use at least two other anti malware programs to double check. Use familiar ones such as Norton, or bit defender, or Kapersky and most can let you do free scans. Don't keep them all on the computer running in real time or that will slow your computer. If it's all clear tell your mom to tell you if the computer is acting in any way different. Be sure she has a good firewall up in her router. (preinstalled usually). You can also set her computer to not let anyone take remote control of it. I'd do that too in case she forgets because these guys always come back to victims and try to get even more money.
If she has a system image or if its not too much hassle the best thing would be to reinstall everything. I know it's lots of work but these people are sophisticated idiots,. if you know what I mean. Tell her it happens to the best of us and not just the elderly. good luck! Rob