Application comes to a halt - Recent developments

For the last 2 weeks once a week we get a huge number of database connections and application is hung.

No one can login into the application.

I can login as system but cannot login as apps. It just waits.

This is a small e-biz system.

Database - 11.2.0.1

Apps  - 11.5.10.2

Users - 50 usrs

Size - 300 G

No diagnositc pack as it is stable but since 2 weeks this is happening.

I see apps connections on the database as 400+ and keep increasing. Normally it is 40 - 50.

the only change is we implemented a scanning solution  based on SOA and weblogic and they also connect using apps.