Galeck1947 appears to be living in some sort of delusional state!
The browser most likely to succumb to external attacks has always been Internet Explorer. That's because (a) it's still (regrettably) the most commonly used browser and (b) it's produced by one of the world's most pathetic software companies, i.e, Microsoft. (Great marketing, constantly lousy software!).
Opera is a good (and compared with any version of Internet Explorer) a relatively secure browser. However it only has a fairly small fan base so it's unsurprising when a website only receives a single complaint about incompatibility. It's still far more likely that your problem lies with the Asda website than with the Opera programmers.
However it might be worth trying one of the two web browsers which nearly all of the 'regulars', here in AB's Technology section use. Most people around here (including me) use Firefox:
http://www.mozilla.org/en-US/firefox/new/
but Chrome has many fans as well:
http://www.google.com/chrome
Chris