[URGENT] Undetected keylogger! Help please!

Hi!
I have a purchased version of avast internet security (on a different account, not this one).

I have reason to believe I have a keylogger or a similar password-stealing virus on my computer.
My Rockstar account has logged in from a different location 2 times today and 5 times during the last month. After every time this has happened, I have changed my password. Passwords were complex.
I also made a thread on another forum (http://linustechtips.com/main/topic/396634-rockstar-account-keeps-getting-hacked-help-please-this-is-urgent) and a Rockstar Support ticket (https://support.rockstargames.com/hc/en-us/requests/4162349).

I ran a full avast scan and a full Anti-Malware scan and nothing came up.
Please help.
Thank you very much.

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