There are some misconceptions on privacy protection provided by the web proxy. Some people think anonymous means he is not traced anymore if he uses a web proxy.
This is not true at all.
Firstly, the web proxy site still keeps a record of your activities. The logs usually can be used as court evidence. Basically, the server that hosts the web proxy sites, by default, will write some access info (usually, your IP, your OS, browser…) in the log file. It is up to the system administrator when to delete or how often to rotate (i.e., delete automatically after how many days) them.