Profits fell to £14m compared with £32m a year earlier.
That fall is partly due to the costs of last year's serious cyber attack,  which cost the company £42m.
Dido Harding, TalkTalk chief executive told the BBC: "We have significantly increased our spending on security. We take this extremely seriously."
Talktalk lost 101,000 subscribers in its third quarter after the attack, which resulted in the personal data of nearly 160,000 people being accessed.
The data haul netted email addresses, names and phone numbers. 21,000 unique bank account numbers and sort codes were accessed in the attack.
There have been six arrests in the UK connected with the hacking, all of them of individuals under 21 years old.
Ms Harding said: "I am actually very encouraged by the way the business has bounced back so strongly in the last quarter.
"The customer base has really stabilised and this is testimony to the fact that our customers really appreciated our open and honest approach and how we tried to look after them through the cyber attack."
She added that Talktalk's customer "churn" - the turnover of customers - has been the lowest in TalkTalk's history, suggesting customers are satisfied with the company's service.
TalkTalk says total revenues grew 2.4% to £1.83bn in the 12 months to 31 March.
Telephone and broadband provider Talktalk saw profits more than halve following a hack attack on its systems last October.