On shut down, popup appears to ask if I want to abort installation

Clicking abort or install fails to identify the application concerned but the system does then shut down. Has been doing this on Mavericks for the past month. The thread below contains some suggestions. I suspect it may be adware but every suggestion to cure the problem seems to be countered by someone else with a warning or alternative. Has anyone else experienced or cured this? Thanks.

https://discussions.apple.com/thread/6568636

Eventually cured the problem with AdwareMedic. Free but it deserves a donation for extreme simplicity and efficiency.