Mac running slow - Install Agent malware cleared by https://www.malwarebytes.com/

iMAC running like a snail. After much searching about and trying the usual clean ups noticed the drain on memory pressure in - Applications/Activity monitor. Install Agent is malware and in was taking up over 4 GB. Ran [Malwarebytes](https://www.malwarebytes.com/) free down load and cleared up this and several other lurking threats including residual MacKeeper stuff.

The problem came on suddenly and not after any obvious downloads by me. No idea how it installed itself.

Sorted :)