If I had a suspicious mind I would think you are trying to hack an environment and are asking how to cover your tracks 
Luckily hiding or removing tasks and events is not foreseen in vSphere through any of the documented API.
You could also consider manipulating the underlying vCenter DB, but I advise very strongly to not even attempt that.
My best bet, but I haven't tried this for 'hiding' columns, is to manipulate the columns that are displayed in the Tasks & Events tab.
See KB1030614 for more details.