1.Try to use Mozilla Firefox or opera or Apple safari as they have very few security vulnerability as compared to the Internet Explorer 7, which is full of well known security vulnerability. Although I have never tried Internet Explorer 8.
2.Never download or activate the grease monkey extension in Mozilla Firefox while orkuting because it may run malicious Java script without your permission leading to your private data export to the hacker.
3.Never click on malicious link or catchy photos from inside your Orkut windows as they lead to almost most of the Orkut hacks.
4.Try to use gmail with your Orkut account although you can use yahoo or AOL or other e-mail ID’s but it will increase the number of SSL handshake although their is nothing wrong in doing that but if you can do it with a single SSL handshake why their is need for multiple.
5.Use SSL mode with the E-Mail account associated with the Orkut.
6.Clear your account history,cookies or files from the browser after you are done with orkuting.
And even after taking every precaution if you are hacked do the following :
1.Report it to the Google Abuses.
2.Tweet this to the Google.
3.Launch an NCP.
4.Change your password and recover your Orkut ID.