Disappointed in Norton Internet Security

Looking for some advice.

I've been using Norton Products for over 10 years.  On two machines (in different locations) in the last six months problems have arisen with malware that has caused file corruption.

There has been no appreciable change in internet use on these two machines (one is for a senior who only uses the machine to check e-mail and the stock market).

Is Norton losing it's effectiveness?  Why are these threats coming through and why did I need to use a product that is a competitor to Norton to fix the problem in one instance?

Seriously considering looking for Internet Security elsewhere.

EVERYTIME the machine is started up I ensure that definitions are up to date and instigate full scans on a more frequent basis than Norton automatically runs.