This is getting infuriating as it obscures part of posts and text making it unreadable. Inside the square it is like a colour TV going completely fuzzy with nothing identifiable in it like shapes or text etc. It is certainly exacerbated/triggered by animated avatars or animated signatures. I don't get it on any other internet sites or in any local applications on the laptop. The interference seems to be square shaped, about 3 to 4 inches square and flashing and is not always in the same place but mostly on the left hand side of the screen. Once it starts it is difficult to get rid of. For example in typing the title to this thread the ability to type text seemed to be switched on and off in time with the flashing on the screen. Sometimes reloading the page helps, sometimes I have to close Safari and re-open and sometimes turn the computer off and on again. This afternoon it was reading a Jaws post, who has animated avatars in his signature that started it off though it has not always done this. My computer is a laptop Apple Macbook Pro and I use Safari as my web browser. I use McAfee anti virus software which has never, to date, let in any trojans or viruses. Safari version is Version 8.0.4 (10600.4.10.7). I run OS X Yosemite version 10.10.2 and all updates are installed. Memory is 16Gb and the processor is 2.8 GHz Intel Core i7 and the computer was new in April 2013. I am with Virgin cable with 50Mb broadband. Any suggestions or help to resolve this would be much appreciated!