To remove fake PayPal alerts from Google Calendar, first delete and report the event as spam by opening the event, clicking "More," and selecting "Report as spam". To prevent future alerts, change your calendar settings to not automatically add invitations from everyone; instead, choose "Only if the sender is known" or "When I respond to the invitation in email".
Remove and report the current event
Click on the fake event in your Google Calendar.
Click More actions (the three dots icon) in the top right of the event window.
Click Report as spam. This will delete the event and help Google learn to block similar future attacks.
Adjust settings to prevent future spam
Open Google Calendar on a web browser and click the gear icon in the top right to open Settings.
Go to Event settings.
Find the dropdown menu for "Add invitations to my calendar".
Change the setting from "From everyone" to either "Only if the sender is known" or "When I respond to the invitation in email".
Also consider checking "Events from Gmail" at the bottom of the Event settings page and unchecking "Automatically add events from Gmail to my calendar" if you don't want events pulled from there automatically.