This is not supposed to occur but both yahoo and hotmail have updated their e mail features and I think mobile phones like iPhones have problems accessing yahoo mail on browser mode unless you download the mail app it's the same for android.
To answer your query the only way to find out is to scan your Oc with some av or search in google.
False alarm.
Today I'm not experiencing the same problem.
Suspect it was the silly ad that appeared before the login screen appeared. I hate those irritating ads that cause such problems. I think it was a Canon ad & the fact that they discontinued the feature that hijacked people to youtube must be because they received complaints
Advertisers should keep it simple if they want people to look at their ads