Open door as in letting anything in. Google needs to certify apps. Not that that completely stops malware from occurring, but it would be a start.
Android Malware Sees Explosive Growth – PCWorld Business Center
“Once a developer has signed up to the Android Marketplace, which costs just $25, they can start releasing software straight away and there are no checks on the apps they create.”
Another problem is that you can easily publish apps anonymously, which makes it very hard to track down an offender.
“Apple’s way of doing things is expensive but effective–having people check over every app that’s released is labor-intensive. However, Google’s approach provides significantly more freedom and openness, and ultimately more customer choice.”
I agree on the last point, but Android Market is also risking being seen as a trash heap long term.