how can I get into IIT ??? should I write only jee mains or both jee mains and advance?? which IIT is having Cyber security related course ?

You have to qualify both for getting into IIT

First you have to clear the mains with good score for NIIT  you should write Advance for IIT

IIT delhi i guess

In order to get into IITs you have to appear for both JEE Main and Advanced exam. You have to qualify JEE Main exam first then you have to clear JEE Advanced exam.

IIT Delhi and IIT Kanpur provides course in cyber security.

You can also follow below strategies to crack your exam-

Choose Proper Study Material: It is a common misconception among aspirants that preparing from a number of books will help them in getting good marks. The truth is that referring the right books only will aid you in securing high. Don’t run behind multiple study material to prepare for JEE Main.Students should choose books that cover entire JEE Main Syllabus and are as per JEE Main Pattern. Suggesting the books for preparation of Mathematics. Complete Mathematics by McGraw Hill Education Pvt Ltd., Coordinate Geometry by S.L. Loney and 103 Trigonometry Problems by Titu Andreescu & Zuming Feng are some of the good books that JEE aspirants can refer.

Strengthen Important & Key Concepts: Students appearing for JEE Main should know that not all topics carry equal weightage of marks. Some topics carry more marks, while others don’t. Devoting much of your time on such important topics is recommended. You just need to identify such topics and practice them more.

More important topics subject wise are as follows:

Physics: Newton’s Laws of Motion, Work Energy Power, Conservation Laws, Rotation Motion, Electrostatics, EMI, Heat and Thermodynamics, Nuclear Physics and Radio Activity, Semiconductor

Chemistry: Redox Reactions, Electro chemistry, Chemical Kinetics, GOC, P Block Elements

Mathematics: Conic Section, P&C, Probability, Quadratic Equation, Definite Integration, Differential Equation, Vector and 3D, Complex Number

Time Management:

Performing well in the entrance exam depends largely on strategizing the flow and proper time management. You should decide well in advance how much time you are going to give on each subject, based on your strong and weak points. With proper time management, you will surely save yourself from the panic during the actual exam.

Solve Previous Year Papers

Solving previous year papers is the most important and required thing to do if you want to excel in JEE Main. Itwill provide you an insight into the type of questions, marking scheme and time duration. Solving these model papers will give you an idea about how the actual entrance exam will be.