That is not p99 files related,. I strongly suggest you run antivirus, anti malware, anti spyware asap.
Change your passwords afterwards. If what you posted is true, I'd be sketched but I know for a fact it's not project 1999's fault.
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Also turn on the steam authentication code email thing.
https://support.steampowered.com/kb_...1266-OAFV-8478
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Make sure your passwords are all unique and strong...
https://passwordsgenerator.net/
example: LF8Qhm4UabnZupBC