Security is something you need to consider anytime you embark on a grow. If you need any convincing watch Lock Stock and Two Smoking Barrels or read some of the tales in the stories section.

The first thing to remember is that the fewer people who know you are growing the better. The temptation is to tell all your mates and bask in the big up glory, but you should only tell people who need to know and make sure that they understand to keep it to themselves.

If you are growing in a shared house or flat MAKE SURE that your housemates are cool with the fact that you are breaking the law. They may agree when you ask them, but beware the power of cumulative paranoia and use your judgment. Make sure you have a lock on your bedroom door. This is an important legal point as it means that only you are liable for what goes on in that room.

Any light leaking out may be a bit of a giveaway so get some heavy curtains over your windows.

The other thing you may need to be concerned about is the smell especially when flowering, The best thing you can do is vent the air from your growspace directly outside, probably not a good idea if you are on the ground floor though. Chimneys are very good for this purpose. If outside ventilation is not an option then a ionizer may help to reduce the smell.

There are some things that you probably do NOT need to worry about, but may do so anyway.
Electricity monitoring, if you only have a small setup (up to at least 1000 watts) the increase in electricity will not be enough too look suspicious.

Helicopters with infrared cameras. The police do have these, but they are used for tracking fugitives at night. As far as I know they are not used to catch Cannabis growers in this country.
Your phone being tapped, this is very expensive for the the police to do and highly unlikely for someone just growing for their own personal consumption.

Internet security

Be very careful with e-mail, It can easily be read by bored system administrators or hackers or even the police without too much trouble. If you want to send e-mail specifically about cannabis growing. I suggest you use PGP which is a free encryption program.