What is PUM.Hijack.StartMenu?
PUM.Hijack.StartMenu is mainly caused by adware/potentially wanted program or even malware. It is noted as PUM shot for potentially unwanted modification. This detection means there will be modification on your start menu settings or there will be browser hijacker associated with those changes.
Please keep in mind that malware will gets in your computer via infected software downloads and malicious websites or pop-ups. It is always alongside with other unwanted programs and then starts to cause a lot of troubles. You should be careful with your online activities in case of being infected.