Is malwarebytes enough, or should I just reformat the hardrive and reinstall the operating system?
Antivirus solutions can help in a lot of cases. But they don't know all malware either because malware is continuously evolving and antivirus is just trying to catch up. In any case you should not trust an antivirus running inside the OS too much, because if malware is active the OS cannot be trusted any more. thus you should it least run antivirus from a clean system (they often offer a bootable system).
Also, note that even after reinstalling the system you cannot be sure because in theory malware might hide inside the BIOS/UEFI firmware on the mainboard or more likely it still hides in files you have restored from a backup.
I have been a victim of identity fraud. I need to find out the origin of this. Someone has applied for a credit card in my name, ...
There are so much data leaks today from compromised web sites that it is hard to know where the data for identity fraud come from. But if the credit card was applied for during normal online-banking where only you should have access then chances are high that it was actually a malware on your computer which caused the problem.