Cenvat Credit of ST

yes, you can avail the cenvet credit on security services

As per Rule 2(l) of Cenvat Credit Rules,2004 input service means any service-(i) used by a provider of taxable service for providing an output service or (ii) used by the manufacturer, whether directly or indirectly , in or in relation to the manufacture of final products and clearance of final products, upto the place of removal.

and includes services used in relation to setting up, modernization, renovation or repairs of a factory, premises of provider of output service or an office relationg to such factory or premises, advertishment or sales promotion, market research, storage upto the place of removal,procurement of inputs, activities relating to business, such as accounting, auditing,financing,recruitment and quality control,coaching and training, computer networking,credit rating,share registry and security, inward transportation of inputs or capital goods and outward transportation upto the place of removal.

The defination of input service is broadly in two parts- first main part  and second inclusive part. In the inclusive part of the defination it clearly mention that security service is an eligible input service in relation to " activities relating to business' , hence it is elegible input service for cenvat credit.

Yes, the one can avail the benefit of Cenvat Credit in respect of the service tax paid to the security agency.

CC can be claimed only when the full payment has been made and Invoice has been received.

Please note that, Cenvat Credit is the credit of duty of excise, customs and service tax which can be claimed by the manufacturer of dutiable goods or providers of dutiable services...

Yes. Even after amendments made in the definition of input service, now w.e.f.1.4.2011 Govt.has specificaly covers the Security service as eligible input serivce hence you can take credit of the service tax on the same and can utilise the same for payment of C.Ex.Duty.