Assuming that you're using a Windows PC (rather than, say, an iPad or an Android device), run an anti-malware scan to zap whatever it is that's causing the problem.
If you've
already got the free version of Malwarebytes Anti-Malware on your computer, use that to run the scan. However I no longer recommend that people without an anti-malware program download that one, as it now forces users into taking a free trial of the 'Premium' version, which can substantially slow down some computers. Download and use AdwCleaner instead. (It's from the same software company and just as good):
https://www.malwarebytes.com/adwcleaner/