I would like to add my voice to this as, suddenly, I am having bsdtar CPU issues that exactly coincide with my running of Parallels Toolbox. I haven't run it in several years because it didn't really offer anything useful to me, but just on a whim decided to install it yesterday to see what was new. It went through several automatic updates as it bootstrapped itself to the latest version (according to release notes), and now I have a bsdtar process that is at 99% CPU and has consumed 21h17m of CPU since yesterday. I did not know Toolbox was the culprit, but Googling bsdtar CPU showed this thread as the number one hit.
Into to the bin with that application!
You won't lose a Parallels customer after this because // is too valuable for me and my work. But after what looks like months with this issue based on the comments in this thread, shame on Parallels for leaving such sloppy coding around and not fixing what is clearly a ton of evidence.