I'm not sure what you mean by legal issues, out of all the business related issues of selling software online legal is about 1% of it but here are things that you should take care of to avoid legal problems: Accidental trademark infringement - This is the number one legal issue you will likely face, in fact it's almost a certainty unless you do your homework on your chosen product name. You could end up spending a *hell* of a lot of money to fix this problem if you don't catch it early on and trust me if you don't catch it the offended party definitely will. Remember that selling online is selling globally so the research you do here will be time consuming and worth every second you spend on it. Essentially if you can register your chosen product name as a .com domain name you've cleared at least half of the research you need to do because anyone who is anyone with a serious business selling software will have already registered a trademarked name as a .com domain. Be sure to check for variant but phonetically similar spelling for similar products, examine the US patent and trademark office online site (doesn't matter if you are in the U.S. or not, that's where the lawsuits will come from most likely since online by nature is selling into the U.S.). Proper license agreement created by a real lawyer who specializes in it for your jurisdiction. Export restrictions - your software may (almost certainly does) contain 3rd party or lower level software libraries with export restrictions, make sure your payment processing company can be set to filter out purchases from restricted countries. Potential patent infringement (unlikely but it *is* a possibility depending on the type of software and industry). And of course all the little business issues that might crop up and land you in legal trouble like income tax, corporate tax etc etc.
"It's so simple to be wise. Just think of something stupid to say and then don't say it." -Sam Levenson