(Adds details of Facebook probes; other companies under investigation)
DUBLIN, Feb 28 (Reuters) - Facebook's lead regulator in the European Union expects to conclude the first of seven investigations into the company's use of personal data this summer and the remainder by the end of the year, Ireland's Data Protection Commissioner said on Thursday.
The commissioner's office last year launched three investigations into aspects of a massive cyber attack in which hackers stole login codes that allowed them to access nearly 50 million Facebook accounts, including 3 million in Europe.
Since then it has launched a separate probe into "a large number of other breaches," including Facebook's disclosure in December that a bug may have exposed private photos of up to 6.8 million users.
The other probes relate to complaints by users in relation to how Facebook processes personal data.
"We are looking at different aspects of the collection, the transparency and the use of data" at Facebook, Commissioner Helen Dixon told Ireland's RTE radio in an interview.
"I think the first of those will possibly conclude over the summer - that is our anticipation - and further of the inquiries will conclude in the latter part of the year," she said.
The commissioner is also probing Facebook subsidiaries WhatsApp and Instagram as well as Twitter, LinkedIn and Apple in relation to their processing of personal data and the transparency of their data processes.
All of the inquiries should reach the "decision and adjudications stage later this year," Dixon wrote in her office's annual report, which was published on Thursday.
Ireland hosts the European headquarters of a number of U.S. technology firms. Under the European Union's General Data Protection Regulation's (GDPR) "One Stop Shop", the Irish commissioner is also the lead regulator for Microsoft, Dropbox, AirBnb and Yelp.
To oversee its increased workload, the commissioner's office expects to hire 50 staff in 2019 to bring its total to around 165, the annual report said. (Reporting by Conor Humphries; editing by Jason Neely and Elaine Hardcastle)