When I use Android in business I have some secret data on my phone. So if I lose my phone this can easily be stolen.
Is there any way I can secure my phone? E.g. adding password for unlocking it. Any recommendations? apps? or best-practice?
Check out a piece of software such as Mobile Defense which gives you remote tracking and wiping of your phone.
You should also be able to add a lock-pattern that makes it slightly-more-difficult to open the phone
The most common way to hack your phone is thru insecure WiFi spots. (Mark Zuckerberg was hacked that way.)
I'd recommend to install Y5 application, which enables WiFi only for spots you trust.
The best way to protect your phone is to encrypt the whole data on it. I know Nexus devices have option to encrypt devices under security settings. What this will do, is every time you boot up your device it will ask for your password, if you don't know it, you will not be able to recover any data on your phone.
You will need to set up some password or lock after you turn of your screen as well, so no one can access your phone if you leave it on table or somewhere else.
If you are often using public access points to connect to internet via your Android device, you should always use https sites.
Most common attacks against smartphone users are man in the middle attacks, this will allow attacker to intercept your session with the current server you are gaining informations from (for example Facebook) and it will be able to login to your account and make changes to your account, post on your behalf etc etc, there is no good defense against this, but you can use DroidSheep Guard.
It will detect if anyone on the network is using this kind of attack, and if so, it will automatically disconnect you from that network, therefor preventing an attack.
There are also some viruses being made lately against android devices, which can harm your device in different ways, I have found out that the best thing you can do against this is, use only play store to download your apps, and check what other people say about application, before downloading it,a lso latest android update has additional security, so if you are installing app from other sources, it can check that app for any malicious code in it.
I don't recommend installing antivirus software on android device, it won't help much, and it will slow your device.
I hope this will be helpful for you and others having concerns about this kind of stuff.