Yo Peliwhotsit in da house,
Sorry... right, back to business !
The machine is actually running quite smoothly now so I'm sort of thinking leave it as it is. Putting annoyances aside, is the security of my machine compromised, such as for online banking?
The safest thing is to assume YES.
The fact that this thing is affecting your web browser means its doubly safe to assume YES.
But also, how do you know there isn't something else lurking ?